Iphone 4 won't update past a 7.1.2 I have a IPhone 4  model number A1349 an it won't update past a 7.1.2 it says my software is up to date but I know the latest software is at the least a 8.4. 
Why is that?
The latest iOS version supported by iPhone 4 is 7.1.2. There is no official way to install iOS 8 or newer on older iDevices.

You can find a compatability list on Wikipedia.