Upgrade Membership Premium Version 3.5.3.3 to Membership 2.0 Pro

Client site has non-subscription "Membership Premium Version 3.5.3.3" from WPMU Dev installed. I want to upgrade them to Membership 2.0 pro ... what is the best way (correct way) to do the migration? I disabled and temporarily "removed" the old dashboard, and installed latest 4.x version of the WPMU Dashboard... but can not upgrade the Membership or Install Membership 2.0 Pro.

I tried searching support docs and website areas but could not find the information I needed.