the instructions for upgrading vary dependent on the jump that you are making, here's my understanding. And my suggestion based on what we do is to put together a step-by-step implementation plan so that you don't forget anything when you're doing it on prod. Also, we have a test plan that we've built up for our specific deployment that we approve on dev prior to doing anything on prod.
1. from 9.0.x to 9.0.6 - uninstall primary and then install new version on primary. New version will be pushed down
2. from 9.0.6 to 9.2.3 - uninstall primary and worker software via control panel add/remove programs. Install workers and then install primary
3. from 9.x.x to 10 (clean install) - take a backup of prod. uninstall primary and workers. delete the Tableau working directories. Install new software. Run a restore.
P.S. I am moving this to the server admin part of the forum.