The most important step is testing. Set up a box (it can be virtual) that is as similar to your production server as possible. Save your $DLC/properties somewhere if you're using them. Upgrade OpenEdge. You'll need to convert the databases and update the VSTs etc. Recompile the environment. Test everything is working.
Of course the process gets a lot harder if you add more steps. So moving to Type II storage will need a dump and load. Moving to a new server makes some things easier, and others harder.
But above all, I can't stress this enough, test, test, test.