iPhone 4

I have an iPhone 4. I set up a whole new iCloud account with it as well and was disappointed at the fact that I'm not able to download basically any apps. Because it has to be updated to an iOS 8 version. But when I go to the settings on the iPhone 4 for software update it says up to date. Which it is updated to Version 7.1.2 (11D257). I want to update it and use my old phone number on this phone. HELP ME!!!! SINCE Y'ALL COULDN'T HELP ME GAIN ACCESS TO BOTH OF MY OLD EMAILS!!!! PLEASE AND THANK YOU IN ADVANCE