Once you have followed the details from http://www.formymobile.co.uk/Dismantle/w850disassembly.htm to the point of all 4 screws are out and you have completely detached the front cover you simply need to push the glass out. It is only held on my double sided tape. I pushed carefully (inside to out) and managed to retain the tape in place to stick my replacement in. Good Luck
Rick K
June 2008