Hi how do I update my iPhone 4 ios

The November 3rd GPS issue is not applicable to the iPhone 4.

Update your iPhone or iPad software to avoid issues with location - Apple Support

The iPhone 4 can not be upgraded beyond iOS 7.1.2.

The GPS rollover doesn't affect the iPhone 4, it affects the iPhone 4s and iPhone 5 aswell as several older iPads, you do not need to worry.