0) Backup old machine by going to File > Backup (which saves the bills.rbi file). Then close the program and copy/zip the entire RTGData folder from the old machine (default location is C:\ProgramData\RTG\RTGData, but check the location from Setup > Database)
1) Install RTG Bills on the new system by running the Bills.exe installer.
2) Activate RTG Bills by going to Setup > Licensed Users and entering your activation license details.
3) Restore the Backup from File > Restore a Backup, then choose the bills.rbi file from earlier.
4) Close RTG Bills program.
5) Copy over the entire RTGData folder from the old machine (default location is C:\ProgramData\RTG\RTGData, but can be changed from Setup >Database)
6) Test to make sure reports run etc (custom reports require the files from the RTGData folder E.G. reportC301.rpt)
Note: RTG Bills seems to only run properly for the Windows the user it is installed on, even though it stores the database in the C:\ProgramData folder which is accessible to everyone.