Usually there is a small plug under the handle on the lever which comes out and behind which is a hex grub screw. You need the right size hex tool to do this. Once that is out the lever should come off the body of the tap - but do turn the water off first!
You will then need a large spanner to unscrew the top, under which is the cartridge causing the problem. This needs to be replaced.
L J B, January 2023
