Well you'll need several things in order to replace JUST the glass on any iPhone starting from Iphone 4.
First you'll need to heat up the screen so that the loca (glue) get soft. than, while it's hot, take the glass away. easiest would be to use a molybdenum wire. insert it between the glass and digitizer.
When the entire glass front is out than you'll need to clean it. i use denaturalized alcohol to clean away most of the loca. use a razor blade to scrap it of (gently) at the end use acetone to finnish the cleaning. My experience is to remove the backlight since it's gonna soak any liquid and get damaged.
When the screen is clean you'll need to put some new glue and than the new glass. There are molds to use but if you don't have one you'll need to try to be precise. if you are unsuccessful doing so you'll have problems with the calibration between the digitizer and lcd.
Once you've attached the glass to the digitizer/lcd part and fit it properly you'll neew to use a UV light in order to bond the whole thing together.
reassemble the phone et voila.
I think you should have some previous knowledge about disassemble phones and be sure of what you are going to do before you attack your device.
- heat gun/plate 100 degrees celsius
- a piece of molybdenum wire
- denaturalized alcohol
- the glass
- UV LAMP circa 36w around 3 minutes