2. Connect your iphone to itunes.(make sure you have the latest)
3. Then click on the iphone tab in itunes and hold shift down and press restore. (It sometimes takes a few attempts)
4. Locate the giffgaff ipcc file and click on it (if you cant find it make sure that your looking for the ipcc files not the iphone software file, this can be found in the bottom right hand cornor of the screen.)
5. Bam ! It will update the file. Then turn your phone off and on again
Or if its jailbroken just goto cydia install sbsettings then swipe top of your iphone screen it will display a few things like turn on and off 3g look for a button with more on it press that then go fown to system options then click custom carrier. Put what u like in there then respring phone. Simple!