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":
We are pleased to announce availability of Beta software for 16.6.3.
16.6.3 will be the second rebuild on the 16.6 release train targeted
towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are
looking for early feedback from customers befor...
Introduction Featured Speakers Luis Espejel is the Telecommunications
Manager of IENova, an Oil & Gas company. Currently he works with Cisco
IOS® and Cisco IOS XE platforms, and NX to some extent. He has also
worked as a Senior Engineer with the Routing P...
In this session you can learn more about Layer 3 multicast and the best
practices to identify possible threats and take security measures. It
provides an overview of basic multicast, the best security practices for
use of this technology, and recommendati...