The best way to move your data files is to: 

1. Create a backup of your database to a flash drive using the "File > Backup" command.

2. Restore the backup on the other computer using the "File > Restore" command from RootsMagic's main menu.

Note for RM3 and earlier:

A RootsMagic database is made up of 33 files, so don't try just moving the .rmg file or your database will not be complete (in fact it won't even work). By using the backup method above, all 33 files are transferred to the new computer.