GigaStudio 3 handles this for you when you install.
If you want to be completely safe, there is a utility on the GS3 install disc called "GigaClean" that wipes GigaStudio from your system. This is also the cleanest way to remove GS3 completely from your system, including your registration info.
Speaking of using GigaClean (which is a great tool, since it gives you a 100% clean slate), be sure you have all of your registration info stored or backed up somewhere, since you will have to re-enter all of this on a subsequent install of GS2.x.
Not that you'll be likely to desire that, once you've worked in 3.0, but GigaClean nukes it ALL...Quicksound database, registration, everything.