Senior Tech

Okay, I'm new to this.  I have two Ultimate1M and one Super Cart.  All I can do is write new FlashRAMs and install them in the units.  Which .ROM file for the cart?  I think I've found the one for the Ultimate1M.  I know nothing about .ATR files and have no way of moving files from my PC to 8bit.  I've been away from the Atari scene for 14 years or so.  Just trying to get my retirement shop up and running.