LOL don't use screws unless you want massive gouges in the front clam when (not if, when) you rip off the front plate on a kerb or speedbump! use very sticky-backed velcro instead, doesn't damage the car and is cheaper to replace!!!
Really depends on the adhesive used- I tried a few things- and found warm soapy water and finger nails the best- just takes time. Once all was removed I degreased it with some Isopropyl alcohol and suck it back on with tape .