Who can i downgrade my iphone

If you're still on iOS6, you should open 'Settings', 'General' and go to 'Software Update'.
You may also connect the iPad to your computer, open iTunes and Check for Update. iTunes will download and update for you.
If you're on iOS7 and want to downgrade, that's a problem. You need to google this as it is complicated, and probably not possible.

Unfortunetally apple doesn't allow downgrading from iOS7. You are stuck with iOS 7, sorry.

Once you have updated your iPhone you cannot roll back the update. This is the case with iOS7 and downgrading is not supported.

Hope that helps!

Regret to inform you that the upgrades to IOS7 is non-revertible. by default as Apple has stopped signing the older versions. Once you have upgraded your device to IOS 7 you can not go back to the previous version. However there is a way which is non-recommended by apple but still its a tweak that work. If you still want to do it follow these steps:
Step 1: Download The Proper iOS 6 File
Step 2: Plug The Device Into Your Computer, Cancel The iTunes Automatic Sync Process (If It Starts)
Step 3: Do Not Put Your Device Into DFU Mode, Just Hit Restore
· To put your iPhone in DFU mode:
Hold down the home and power button for 10 seconds.
Release the power button while continuing to hold the home button for eight seconds.
This process sets up your phone automatically for a restore. It is not technically required to downgrade to iOS 6. At the same time, using DFU mode will not have any negative effect on restoring to iOS 6. You can use it if it makes you comfortable.
Once your iPhone is recognized by iTunes, simply hold the Alt/Option button on a Mac or the shift key on a Windows machine and click "Restore iPhone..." The option to choose the iOS6 .ipsw file will pop up, the same way it does when upgrading to iOS 7.

Unfortunately, You can not downgrade from iOS7 to iOS6. You can read more about it from the link
http://www.iphonehacks.com/2013/09/cannot-downgrade-ios-7-ios-6-1-3-ios-6-1-4.html
Apple sucks this way.

Downgrade from iOS7 to iOS6 is impossible now.

Unfortunately, you can not downgrade from iOS7 to iOS6.

It can only be done for iPhone 4 or older that were jailbroken on the old firmware, and have SHSH blobs saved.
If you have an iPhone 4 or older device and have SHSH blobs saved for the firmware you want to downgrade to, you can follow this guide:http://www.digitaltrends.com/mobile/how-to-downgrade-to-ios-6/

If you have a newer device than iPhone 4 or do not have SHSH blobs for an older firmware, I'm sorry but you have no way to downgrade...

If you're device is updated to IOS6 you may see some general performance problems because the os is designed to work with a much more powerful iPhone. If you can follow this guide that im linking you can downgrade to the older IOS 5.1.1 and the phone will be much faster.