Official comment
@Paul > The absolute #1 easiest way to do it:
Open rekordbox
File > Library > Back Up Library
If your music is already external or you can manually move things yourself, skip the step asking if you want to gather the music as well. If not, answer yes.
Copy the backup from the desktop (or wherever it was created) to an external drive (make sure it's FAT32 or exFAT so both OS's can read it), and if you backed-up the music, grab that folder from beside the database backup.
If you're done using rekordbox on the PC, deactivate it.
On the new computer, install rekordbox and activate it and start with a blank database.
Open the File > Library > Restore Library and pull it from the backup. Again, if you also had the music backed-up, you can have rekordbox put it back into the new computer at the same locations it previously lived at.
That's it.