where can I find documentation to migrate to 18 from 17
Backup your configuration settings via the web UI then run the update (also from the web UI), you need do nothing else apart from read the release notes and take a look at the forums to see if there's any problems that may afect you.
1. Grab latest update from 17.7, which is 17.7.12_1
1.a. Console option 12, type "18.1" when prompted.
2.b. Reload firmware page, unlock 18.1 upgrade in end-of-life banner message.
3. All done.
Cheers,
Franco