Changing thermostat in a 1995 BMW 318i?

In front of the motor there will be metal housing with two hoses connected to it. That is the thermostat housing.. Once you get the bolts out the thermo should come out without much fuss (take a screwdriver to it and slide it in to pivot it out if needed). Get a gasket with the new thermo throw it on, line it up & re-install the housing cover. I'd also recommend a new housing gasket. You may also want to drain out your anti-freeze to prevent a mess.