Yes, it is a very straight-forward job. I just changed the thermostat on my car a couple of weeks ago. Is your car an automatic or a manual? On the automatic, you probably will have to remove the engine-driven radiator cooling fan to get undisturbed access to the thermostat. You will have to pull out the electrical fan on regardless of transmission.
The thermostat is electrically heated, so it will have a harness you need to disconnect and reconnect once done. By the way, the sucker is expensive: around $65, but the thermostat an a new housing come together as one part.
Oh,, you will also have ot remove the plastic splash guard from under teh engine bay for the coolant to drip out.
I am sorry all tehse pointers are so scattered. RUn an online search for E46 thermostat DIY and you will find step-by-step instructions. I don't think we have a DIY on our forum yet.