Have iphone 3gs need to update ios to 6.0 or later

You can try different ways to update iOS. One of them shows below.

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.

For more methods, check: How to Update iPhone

There are different ways to upgrade iPad. You can follow below steps to update your iPad with ease.

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.

If this method won't work, check: How to Update iPhone

The easiest way for most people to update iOS 10 to iPhone is over the air, directly on their device. It's fast, efficient and simple to do.

1.Click Settings, then tap on General
2.Tap on Software Update.
3.Tap on Download and Install.
4.Enter your Passcode, if prompted.
5.Tap Agree to the Terms and Conditions. Tap Agree again to confirm.
6.Tap Install Now to begin the update.
http://www.leawo.org/tutorial/how-to-update-ios-9-2-to-iphone.html

Of course, there are different ways to update iPad. You can follow below steps to do that.

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.

For more methods, check: How to Update iPad

Here's how-to:
Update the iOS software on your iPhone iPad and iPod touch
video:
Get iOS 7 on iPod Touch 4G and iPhone 3GS FREE AND EASY

depends on the iPad model you have:
For the iPad first generation (A1219) before iOS 5 to update is only possible with connecting the device to iTunes on a computer. Plug it into your computer and open up itunes under devices click on your ipad and then click on check for update.
- but this model supports only iOS 5 !
- NO iOS 6/7/8 !
for all other models:
There are two ways to update the iOS version of your iPhone, iPad, or iPod Touch - via connecting the device to iTunes on a computer
- or directly from within the device, but only since iOS 5 it is possible to update the iOS version without the need to connect the iOS device to a computer (over-the-air update)
just go to: settings - general - software update

- depends on the model of your iPad:
For the iPad first generation (A1219) to update is only possible with connecting the device to iTunes on a computer.
- but this model supports only iOS 5 - NO iOS 6/7/8 !
for all other models:
There are two ways to upgrade the iOS version of your iPhone, iPad, or iPod Touch - via connecting the device to iTunes on a computer
- or directly from within the device, but only snce iOS 5, it is possible to upgrade the iOS version without the need to connect the iOS device to a computer (over-the-air update)
just go to: settings - general - software update

-depends on the iPad model you have:
For the iPad first generation (A1219) before iOS 5 to update is only possible with connecting the device to iTunes on a computer. Plug it into your computer and open up itunes under devices click on your ipad and then click on check for update.
- but this model supports only iOS 5 !
- NO iOS 6/7/8 !
-----------------------
for all other models:
There are two ways to update the iOS version of your iPhone, iPad, or iPod Touch - via connecting the device to iTunes on a computer
- or directly from within the device, but only since iOS 5 it is possible to update the iOS version without the need to connect the iOS device to a computer (over-the-air update)
just go to: settings - general - software update

- depends on the iPad model you have:
For the iPad first generation (A1219) before iOS 5 to update is only possible with connecting the device to iTunes on a computer. Plug it into your computer and open up itunes under devices click on your ipad and then click on check for update.
- but this model supports only iOS 5 !
- NO iOS 6/7/8 !
-----------------------------
for all other models:
There are two ways to update the iOS version of your iPhone, iPad, or iPod Touch - via connecting the device to iTunes on a computer
- or directly from within the device, but only since iOS 5 it is possible to update the iOS version without the need to connect the iOS device to a computer (over-the-air update)
just go to: settings - general - software update

First Generation iPads can use iOS 5
- but iOS 6 / 7 / 8 need an iPad 2 or newer and are not compatibel with first gen. iPhone
-updates can be made in iTunes connected to a computer or under settings - general - software update
Upgrade iOS from within iOS device
(valid for iOS 5 and above)
Since iOS 5, it is possible to upgrade the iOS version without the need to connect the iOS device to a computer (over-the-air update). To upgrade to iOS 6/7/8, simply navigate to Settings > General > Software Update. The screenshot below demonstrates how to do so on an iPad, but this is also valid for the iPhone and iPod Touch.

in iTunes:
How to update to iOS 7