Remove the cap - which covers the end of the axle on the end of the pedal - furthest away from the cranks. From there you should see a lock-bolt or ring of some form. Remove. Then remove the cone. You should now be able to pull the axle free from the pedal body. Clean thoroughly and add new grease and fresh ball-bearings (count how many were in there if possible - just don't try to jam in one too many) and re-assemble. The final adjustment may take several attempts. Don't be discouraged, it takes us all awhile.

This is intended to be done with the pedals removed from the bicycle.