Ok you need to take off the front side pillars (the plastic) , then the side pillars, and on mine there are 4 plastic retainer clips on the back. Then it should come out.
Then you have to remove the old head liner and pad if it is messed up also. Then get some spray adhiesive spray down the headliner board and start in the middle and flatten out towards the ends.
If anyone else has any other precautions, or ideas they want to share plz be my guest. But this is how i would do it if mine where messing up.
Or you could take a can of spray adhiesive cut small holes in the bubbles in your headliner and spray some of the glue into the hole and faltten out. The only thing wrong with this is, it might be streached out a lil bit so it might not smoothen out right.