There is a guide somewhere in the maintenance section.
When I did mine I couldn't remove the headrest but you can peel the fabric back and put two slits in the foam below the headrest to remove the old foam and again in the new foam to refit. Once it is all back together you can't tell.
Sorry just reread your post. It's the top half of the drivers seat cover you want to replace? You will need to remove the headrest then but not sure if this is possible. If you have a full donor seat not just the covers and foam you could swap the top half of the seat over.
