Upgrading from 5.7.1 to 6.2 - any pitfalls?
To migrate a process definition, first migrate it to 5.9 or 5.10, and export it as a .bar file. Then use the guided migration feature of 6.x, described here. This automates the process migration as much as possible, though there are some things that you need to check or do manually.
The 5.x and 6.x platforms are very different, so there is no upgrade route, but rather you do a new install of 6.2. For more information, see here.