That's opening a can of worms, although you'd expect it to be easy being a linux system and all (unfortunately it isn't as simple as typing su & a password at the command prompt ). There are several ways , and quite a bit of discussion as to which is easiest, which is best, etc. The main three methods, to the best of my knowledge (although I'm sure we'll hear about it if I'm wrong), are installing 'becomeroot', installing 'easyroot', or using openssh. There are others (e.g., r&d mode), but those seem to be the most often mentioned.

I've been inclined to go with one of the first two options. But some will swear by the openssh method. If you search the forums for these keywords, you'll see where to get the packages and what to do once you get them. I'd look at them and see which one looks easiest for you to understand and get working quickly and go with that.