Banks A & B are RAM banks (as described in the manual!)....meaning that this is where you will 'store' any programs that you create, BUT will overwrite whatever sound in the location you decide to save your own sound.
You could however, go through the sounds in banks A & B and make a note of the sounds which you are not so fond of, and which you wont mind deleting. Banks A & B can always be backed up as a .MID file in your sequencer, as a safety precaution, or you can simply download the factory patches from the ever so great Access website.
In fact, take a little time to read the manual, as it contains all the information that you need to know, especially questions like the ones you are asking. But if you get really stuck, we are always willing to help.
If you dont have the Virus manual, you could either order another one from Access, or download a copy of the manual in PDF format.
Good luck....and welcome to the forum!
Jason