Alternator question Please help

I have a 94 saturn and I think I need to change my alternator.

Can I do it on my own?

and

How do I know if I need to change it? My battery was low today and I had to have it charged after I left my lights on for about 30 minutes

thanks

Found the problem it was a faulty or bad alternator. My friend and I replaced it and it works fine now.