If you are talking about the motor cooling filter round filter like this here then you must have removed wrong screws. Screws that you want to remove are hidden under clear lenses on the sides of the unit. You will need a screwdriver to remove the lenses (2 latches at the top of each lens). Once you have removed lenses you will see screws (4 or 6 - depending on the e-series model). Remove them and you will have the access to the filter.

Good Luck