Some time ago I wrote about how to change the lens from this Philips SPC900NC webcam to let it collaborate with the DIY FTIR multi-touch project. I dissambled the entire webcam back then, which seems to be unnecessary. You can easily rotate the round grey thing (with all the small lines carved in it) in front of the lens untill it's impossible to rotate it any further. At that point you can use a sharp knife, to pop it off. Than you can unscrew the lens and put the new lens in place.