How do I dismantle leaking single lever basin tap?

I've got a single lever basin mixer tap with the ceramic type valve.
There is a slight leak, from under the dome part that moves when the lever is raised or lowered. The tap works fine apart from this small leak

How do I start to dismantle the tap to diagnose the problem? Is it just a case of pulling upwards?

Regards
Mike.

useally it will have an allen key grub screw useally located under the blue/red badge.
unscrew then the lever will lift off it sits on a square part of the cartridge.

Thanks for your suggestion. I'll examine the tap head and attempt to remove it.