I have an RCX 1.0 set from 1998 and I would like to upgrade the RCX 1.0 to RCX 2.0. Can this be done? Exactly how would I obtain a firmware file and load it? I do have access to the Bricxx Command Center, if required.
The hardware of RCX 2.0 is identical to 1.5, and the only difference between these two and version 1.0 is the charging port which had been removed. So they're compatible and you can indeed use a newer firmware on an older brick.
You may also want to use a compatible, but faster, firwmare from Dick Swan, you'll find it archived here.
As for uploading it to the RCX brick, I think there's indeed an option for it in BrickCC but I'm not too sure where, so I can't help much there. It's probably in the documentation somewhere.