How do I replace the back glass on an iPhone 5?

The antenna and flex cables are untie this glass. I would strongly recommend against prying off the glass directly as it is way too risky

The glass is adhered to the frame using epoxy glue. It does not get softened with heat, so hard prying and scraping is required. It is precision matched and installed using expensive machinery with microns of accuracy, there is no way you can do better than apple, slight mismatch is acceptable. After all, successfully repairing the glass is already an achievement