if you have the little dyson spanner/screwdriver that came with your machine then it is easy to do
use the flat screwdriver shaped end to lift the red or yellow catch on the filter cover and at the same time unscrew the cover in an anticlockwise direction i.e to the left
if you don't have the dyson spanner a small flat bladed screwdriver will do the job equally well
also be prepared for a bit of water on the floor
i put an old towel down first to catch the water then bung it in a wash when i have finished
chris, August 2010