i had to replace mine about 8 months ago because it just broke and started spewing oil. the thing is that it is conveniently located where you cannot get your hand in with the proper tools. what you will end up having to do unless you can figure out a better way is removing the radiator. this only takes about 10 minutes and makes life a lot easier. once you got that out you just unscrew it out of position. the thing about the sending unit was that it had a weird shape so none of the sockets would hold right, you're just gonna have to get it somehow, either with a big ass socket or a vice grips or something. when installing the new unit make sure not to tighten it like a normal nut. the thing is very sensitive and you could brake it installing it too harshly.
i needed my car the day after mine broke and no auto store had the exact part for my car, so what i did was take them my old unit and told them to get me one that matched the thread width. then i just made a little adapter for the wire that plugs into it. all together its a fairly easy install.