Ive changed mine maybe 6 - 9 months ago, and if I remembered correctly. You unscrew the gear knob and be careful of a spring inside, then you will need to unclip the base of the gaiter. You can feel a ring around the gaiter that prevents the leather from coming off, and thats the "ring" you will need to unseat, 6 clips in total I think. Heres the tricky part...The base of the gaiter is held in so tight that Ive damaged 2 of those clips whilst removing my original gaiter.
(Once the clips were damage, it wont hold the gaiter properly)
Luckily, I manage to source a replacement ring from a breaker for ?£7. (On ebay, you cant actually buy the ring itself, you will have to purchase the whole assembly from the breakers and its around £25.)
Hope it helps, if in doubt, use a set of plastic trim remover to gain leverage to free the "ring"