Im gonna give you my similar experience with a broken glass galaxy s3 mini. The glass is glued with a clear adhesive to the screen/digitizer, and is not meant to be replaced. You have 3 options as far as i understood(i am not a professional):
1)Remove the glass and place the new one, using double sided tape to hold it in place. This is the simplest but the results may not be very good.Dust can get in between the glass and the screen and the touch function may not work very well due to bad coupling between the glass and the digitizer.
2)Replace the glass, but use a liquid optically clear adhesive to glue it in place. This is a lot harder, but can give very good results. In my case the first try i used too much pressure on the srceen, and a lot of the glue sqeezed out and i ended up with a lot of bubbles near the edges.I tried again with a little more glue and less pressure, i got near perfect results. The glue also covered all the scratches i made to the screen while i was scraping off the cracked glass. However you mileage may vary and it is very easy to completely fuck it up.
3)Replace the entire glass/screen assembly. If i was doing it again this is the route i would probably choose. It generally is the easiest and most sure to work.It is also the way it was meant to be replaced, as an entire assembly.