With AOL 9.0, you'll have to do it from AOL's software. From what I remember, load AOL and before you sign on, you'll have to go to "setup" (or something along the lines of that).
Then something like "hardware setup" or "configure hardware"
You'll sometime need to select your modem and hit configure, something like that. Ugh, I wish I can remember the exact details.
Then set the volume to where you want it. I'm sorry I don't have the exact directions as it's been about 3 years since I last used AOL. But I bet if you were to click the setup button before you logon, you can take it from there. Again, I'm sorry for the vague answer.