Don't include "if you knew anything about X" in your reply if you're going to spout nonsense. The whole idea behind "Retina" displays is they're an increase in pixel density rather than a simple increase in screen geometry.
The iPhone 4 had a screen with roughly twice the pixel density of the iPhone 3GS and earlier. This is where the "@2x" naming scheme for images originated. The geometry of the iPhone 4's screen was the same as earlier phones but with a higher pixel density. The iPads had the same sort of density increase.
The geometric difference between the iPhone 5 and 6 over the 3GS is immaterial. They maintain the high pixel density. The only place where a developer will care is if they have static images that fill the display. They'd need larger ones for the iPhone 6 and 6+.
For a majority however the increased screen geometry will simple mean more content space. Apps tend to have fixed elements in portions of the screen with flexible space in between. The new iPhones will just see a bit more flexible space.
An icon for a button won't need to change unless you want to make it bigger in proportion to the screen. In fact iOS 8 (the OS on the new phones) has several new view classes that allow them to adapt easily to different screen sizes. This is a feature OSX has had for a long time, the UI can be laid out in relative values so it will be correct no matter the window size or aspect.