CNMathon matteocontrini's advice is sound, and you can look at what I wrote for a similar question upgrading to Beta 9 from Beta 7.
The biggest step here is to backup what you have already. Once you have that, you can recover from just about any problem in the upgrade. The other suggestion is not to do the upgrade live, do it on another area of your site or locally instead, to make sure it works first.
