Not sure what you mean by "upgrade path", but logistically 3.x does require paying for new license(s). FWIW, I migrated directly from 2.6 to 3.1, bypassing 3.0 and 3.0.1.
The documentation you're looking for is probably something along the lines of "Data Migration Guide for LAN Management Solution 3.1", which lists topics such as "LMS 2.6 or LMS 2.6 Service Pack (SP1) to LMS 3.1":
