upgrade path
I have a "Compact Control Builder AC 800M 5.1 Getting Started" manual here, that has a good upgrade path chart on page 137 (appendix C). Shows the path from 3.1 as:
3.1/x-->3.2x-->5.0.1 or 5.0.0 -->5.0.2/x--> 5.1
I would verify this with ABB tech support, and see if there is some way to shortcut the process....