In the Unified Manager, click on IP Music. You'll have to click on Tools (I think), then select BCMAmp Ctl. That will bring up the BCM Amp application which will let you upload files to the system.
Biggest issue is that the files have to be small (5MB or less I think). You'll have to change the files to make the size small enough to upload. I'll usually set the files to 8 bit mono - figure the people listening to it are on a phone line, so it sounds fine.
When the playlist is built, set your music source to BCMAmp, and you're off and running.