First, make sure that you don't have any ATL cards in the old Legend system. If you do, you can't convert the current translations, you would need to reprogram from scratch.
If the current cards are all supported, use WinSPM to download the current translations, use the "convert" utility if WinSPM to change the translations to be compatable with the Magix release you are installing, and upload them to the Magix processor. Hopefully, you have a spare cabinet and power supply, so you don't have to take the system down during the upload process.
Then change the processor and you should be good to go. The port license card can be swapped from the R1 to the R4 with no problem.