I'm no longer on the network that I downloaded iTunes. Need to download the new update so I can back up my iPhone.

There are several methods to update iPhone and following below steps can help you to reach this aim easier.

How to Update iPhone Software Wirelessly If a message says that an update is available, you could then click "Install Now" button to start to update your iPhone iOS software. Also, you could manually check whether there is an iPhone iOS update or not on your iPhone. The below steps would show you how to update iPhone software wirelessly:

1. Before you update iPhone software via WiFi connection, you need to make sure your iPhone has enough storage and battery to support the iPhone update.
2. Connect your iPhone to a WiFi network.
3. Tap "Settings > General > Software Update" successively.
4. Tap "Download and Install" option when your iPhone has detects an update available. If a message asks to temporarily remove apps because iOS needs more space for the update, tap Continue or Cancel. Later, iOS will reinstall apps that it removed.
5. Then iPhone would start to download and install iOS update immediately. You only need to wait for the update complete.

How to Update iPhone Software with iTunes If you can't update iPhone iOS software wirelessly throug WiFi connection, you could give iTunes a try. As the all-inclusive iOS device manager center, iTunes provides multiple effective assistances for you, including: backing up iOS devices, restoring iOS devices, transferring iOS data files, and updating iOS devices. You could follow the below steps to learn how to update iPhone software with iTunes in detail:

1. Install the latest version of iTunes on your computer.
2. Connect your iPhone to your computer via the USB cable.
3. Open iTunes and select your device.
4. Click "Summary > Check for Update".
5. Once iTunes detects the available update, click "Download and Update".
6. If asked, enter your passcode. Then iTunes would start to update iPhone iOS software. When it's finished, disconnect your iPhone with computer.

For more methods, check: How to Update iPhone

Before update your iPhone

• Back up your device.
• Check enough available space to install the update.

Update iPhone wirelessly :

• Go to Settings > General > Software Update.
• Download and Install the update.

If you are looking for updating with iTunes then follow Mac Support .

If you want to sync apps to new iPhone, you can take advantage of the "Automatic Downloads" function of iTunes. You only need to tap Settings > iTunes & App Store, and locate AUTOMATIC DOWNLOADS, then turn on Apps and Updates. Finish the steps on your iPhone so that you can get apps on the other device when you finish a download on one device.
http://www.leawo.org/tutorial/how-to-sync-iphone-apps-to-ipad.html

1. Does your device support iOS 7?
iOS 7 is supported by iPhone 4, iPhone 4S and iPhone 5; iPad 2, third and fourth-generation iPads, iPad mini; and the fifth-generation iPod touch. Also, certain features of iOS may not be available on all devices. For instance, the iPhone 4S doesn't support features like AirDrop and live filters in the camera app. The iPad 3 also doesn't support AirDrop.

2. Backing up your device
If you don't regularly backup the data on your iPhone or iPad, now is a good time. You'd like your favourite apps and settings to transition to iOS 7 and for that you'll need to take a backup.

You can take a backup your device in two ways, backing up to iCloud (Apple's servers) or by backing up data to your Mac or PC via iTunes.
3. You can either install iOS 7 directly to your iOS device through an over-the-air Software Update via Wi-Fi or connect it to your computer and install the update through iTunes.

To upgrade over the air, go to the Settings app, tap on General and then on Software Update. Wait for the update message to appear and tap on Download and Install.

If you want to install the update through your PC or Mac instead, connect your device to the computer and wait for iTunes to open or fire it up manually. You'd typically get a software update prompt but if you don't just go to the device Summary page by clicking on the name of your iOS device, and click on the 'Check for Update' button, and click on Download and Update.
4. After updating your iPhone to iOS 7, you'll see a welcome screen, post that you'll be prompted to enable Location Services, following which you will get a page where you can select whether you want to set up your iPhone as a new phone, restore from an iCloud Backup or restore from an iTunes Backup. You'll need to enter your iCloud credentials and stay connected to a Wi-Fi network if you select the iCloud backup option or ail need to connect your phone to your computer if you select the iTunes option. After a few more prompts asking for your iCloud and iTunes credentials and pages displaying terms of use, you'll finally see your Home screen with a brand new OS.

you can check apple accessories for iphone , ipad,ipod by copying link given into browser:
smarturl.it\appleaccessoriess

What's the current version of your iPhone?
iOS4? or you want your iPhone back to iOS4?
If you do not back up for IOS4, you won't update it to the version before iOS 6 now, as APPLE has stop support the Verification of old version
I your current version is iOS 4 and you want to update it you can update by iTunes easily. Just download newest iTune on PC and link iPhone to PC, then it will notice you for the update information.

Turn off "Airplane Mode".
Connect your iPhone to iTunes on your computer, and look for any software updates for the iPhone; if there are any, download the update, and let iTunes update your iPhone.

Do you have the correct ID/password for the network that you're trying to "join" ?

There are many ways to update iPhone. The easiest way is to update via air. Certainly, iTunes is another great choice. Just follow below steps.

Update iPhone to iOS 12 via Air
1. If a pop-up panel shows you that iPhone latest version iOS 12 is available, you can click on the "Install Now" button to start to update iPhone to iOS 12.
2. It is also accessible to check out if iOS 12 is available manually now. The following steps will instruct you to make it.
a) Connect iPhone to a good Wi-Fi network and make sure your iPhone storage is enough. You also need to ensure that the battery of your iPhone can support the update.
b) Click on "Settings > General > Software Update> Download and Install" successively and iPhone will start to download and install iOS 12 right away. Wait until the update is completed.

Update iPhone to iOS 12 via iTunes
1. In order to use iTunes to update iPhone to iOS 12, you can first download iOS 12 IPSW file from this website (click here).
2. Run the latest version of iTunes on computer and insert iPhone to computer.
3. Click on iPhone icon on iTunes interface and then hit "Summary> Check for Update".

4. Choose the IPSW firmware file that you have downloaded beforehand by performing the following actions in iTunes: >
Mac: OPTION + Click on the "Update" button in iTunes
Windows: SHIFT + Click on the 'Update' button in iTunes

5. Navigate to your computer folder to choose the IPSW file and then click on "Update" button to confirm that you would like to install iOS 12 in the pop-up panel.

6. Wait until the update is over and iOS 12 is installed on iPhone. In the end, your iPhone will reboot with iOS 12 successfully installed.

For more details, check: How to Update iPhone to Latest iOS 12

Hi,
Here u can follow the steps

Step 1: Make sure you have downloaded the latest version of iTunes if you haven’t already. Download iTunes 8.2 from the link given below.
Step 2: Now connect your iPhone with your PC. You must connect it to a single usb port on the backside of your computer. Do not use any usb hub or the ports in the front as this could cause an error during update process.
Step 3: Start iTunes 8.2. Sync your iPhone with your PC so that iTunes backs-up all your important data including settings, apps, music, contacts and photos.
Step 4: You will now have to download a custom cooked firmware for your iPhone version (2G or 3G). I can’t post the download links for these files for the reasons you all know very well. Just Google “iPhone 2G Custom 3.0” (If you are using iPhone 2G) or “iPhone 3G Custom 3.0” (If you are using iPhone 3G) and use one of the torrent links to download the custom created .ipsw file.
Step 5: Once you have downloaded the required .ipsw file, Copy/Paste it into this location:
“C:\Users\[username]\AppData\Roaming\Apple Computer\iTunes\iPhone Software Updates\” (Windows 7)
“C:\Users\[username]\AppData\Roaming\Apple Computer\iTunes\iPhone Software Updates\” (Windows Vista)
“C:\Documents and Settings\[username]\Application Data\Apple Computer\iTunes\iPhone Software Update\” (Windows XP)
Step 6: Restart iTunes. You will now be prompted to install this firmware you just download. Just close this prompt dialog by clicking on “x” from the top right-most corner of the window.

Step 7: Now you will have to restore your iPhone to this custom firmware 3.0 that you just downloaded. Click on your phone from the sidebar in iTunes to get to this screen as shown in the screenshot below:

Now press and hold left “Shift” button on the keyboard and then click on “Restore” (Not “Update) button in the iTunes and then release the “Shift” button.

This will make iTunes prompt you to select the location for your downloaded custom firmware 3.0. Select the downloaded .ipsw file and click on “Open”.
Step 8: Now sit back and enjoy as iTunes does the rest for you. This will involve a series of automated steps some of which are highlighted below:

Don’t do anything silly at this point. Just wait while iTunes installs the new firmware 3.0 on your iPhone. Your iPhone screen at this point will be showing a progress bar indicating installation progress. After the installation is done, iPhone will restart automatically and you should now have a fully unlocked and jailbroken iPhone 2G. iPhone 3G on the hand will only be jailbroken, not unlocked. iPhone 3G users will have to wait for Dev-Team to release ultrasn0w on Cydia in order to unlock their phones.
Step 9: Once you are done with the unlocking and jailbreak process. You can now restore all your settings, apps, music, contacts and photos to the newly installed firmware version 3.0 by restoring the backup that you made in Step 3 from iTunes.

Feel free to ask me any question here should you run into any problem during the update process.
Disclaimer: This guide is for testing & educational purposes only. I’m not responsible for any loss of important data or malfunctioning of your iPhone.
Download Links:
Download iTunes 8.2
Download iPhone OS 3.0 Custom Firmware (iPhone 2G) [Screenshot]
Download iPhone OS 3.0 Custom Firmware (iPhone 3G) [Screenshot]

/**/ Thanks

Thiru

Have you updated the itunes to the latest version ?

What version are you having now ?

What happens when it "quits"?