I'm new to this but I had my phone jailbroken years ago and they told me I had to stay under Apple's radar so I never tried to get it updated. Now I can barely use any of my apps, for instance I can't FaceTime at all any more. Can someone provide step by step instructions on how to update my phone?
Back up your iPhone with iTunes.
Restore your iPhone with iTunes.
If you want your phone jailbroken with iOS 7.1.2, jailbreak it at this point.
Restore your iPhone from backup.