I am sure this tap is the same as mine, which leaked badly first time out!
There should be a small coloured plastic insert, on the tap that can be prised off. Behind that is an Alan key socket that you insert an Alan key in to undo. This then releases the top of the tap. This exposes a large nut which you undo. Inside this is a plastic insert that needs replacing. Take the insert to your dealer and purchase a new one. Replacement is the reverse procedure!
It sounds complicated but is very easy in practice.