Swapped one on a mated Golf recently, 5min job to swap. Unclip pull out, push new one in and replace clip.
Quote from previous thread ...
one electrical connector to remove, one plastic circlip, pull out sensor, loose a bit of coolant, fit new sensor (making sure it has a rubber seal and that the old one is still attached to the old sensor and not stuck in place), refit circlip and electrical connector, top up coolant. Job done in about 60 seconds. Dont forget to close bonnet. ; )
We didnt top up the coolant as it must have lost no more than an egg cup full. Stuff some kitchen roll under it before removing to catch the coolant.