if its the old type of tap, you need to get the screw out , but if there is limescale there,then the top of the tap will be stuck with limescale too, so unscrew the screw as much as you can , use wd40 spray oil on it , tap the cover up with a small hammer ect" you must that the top off the tap to get the cover off, and you need the cover off to open the body of the tap,to get at the washer. with the water turned off first. to get at the washer, or the only other way is to replace the tap with a new one. and you can take the all of the tap off from under the sink, but try the first way frist,,
l, June 2012