Hi, very straightforward. Open the boot lid, undo the screws holding the latch in place, carefully remove it keeping note of the position of the 's' shaped linkage (which you'll need to unhook) and then remove the lock. Take out the grotty old seal, carefully clean up the painted surface so there's no residue left, fit your new seal and reattach the lock and latch.
Don't buy the seal from eBay as they're much cheaper via VW Heritage-classic parts.
Register Member 829
1980 Mk1 GLi
1980 (1976) Mk1 Junior Cup Replica
1982 Mk1 GTI (pending project)
1987 MK2 GTX