Just did mine 1 week ago
there is a thread on here about how to do it without removing half the engine
you will need to remove the under engine cover and the right hand side splash guard as well as the coolant pipe that runs from the front of the sump to the thermostat
Also take off the turbo to MAF air duct as this gets in the way a bit
access to the stat is improved by unbolting the RHS upper engine mount and lifting the engine
you can finally get to all 4 screws although 1 of them is a bugger and the use of a ratchet ring spanner (torx) would help a lot
a search for thermostat replacement should find the thread in question
just be calm and it works a treat
just to confirm my car now has rock solid temperature (measured via OBD port) but he dash gauge shows no difference.
yesterday did the same thing on our BMW 320d (same engine) - temp is rock steady there too at 91....