How to replace the alternator on a BMW X5?

I have a 2003 BMW X5 and the alternator seems to be the problem. I already changed the battery twice (thinking it was a battery problem), but yesterday, the battery started draining again. Others had told me that it could be the alternator. I've priced the alternators and I would rather do the work myself, but I don't know how difficult this task might be. Any thoughts?How to replace the alternator on a BMW X5?why don't you take it to your bmw service center so they can hook it up to the computer and check where the problem is, and it up to you if you want them to fix the problem or take it somewhere else, atleast you will check out all options before doing anything.