Good question. I have no idea about the changelogs for the legacy branch. I guess not much happened in between so you could just try to change to stable. Or do a test on a separate virtual machine or with snapshots if you can do them.
Of course check you have a working(!) backup before.
If its a business critical installation I would suggest you get in contact with Tinc, or servercow.de, maybe they have done this for a client and can share some tips.