Anthony - upgrading Tableau is pretty straightforward.
For Desktop and Reader, you can simply run the new 5.2 installer and it will install into a different folder from your existing 5.1 version. The new version will become the 'default' version and will be the one that launches when you double-click a twb(x) file. The new version of Desktop will automatically use the existing license key on that machine, so you don't need to do anything special with keys. On the first launch, it will ask for registration information though. Once you install, if you wish, you can then uninstall 5.1 using the Windows Add/Remove Programs Control Panel. No real harm in leaving the older version on the machine for a bit though.
For Server, the steps are a bit different. The recommended steps are:
- backup your existing server (run tabadmin backup, and place the tsbak file it creates in a safe place, meaning not in the Tableau Server directory)
- uninstall the existing 5.1 server (using the Windows Add/Remove Programs Control Panel). This step removes the software, but leaves all your existing content and settings on the machine
- run the new 5.2 installer. It will detect the existing content/settings and automatically import it all as part of the install process.
You don't need to do any returning/reactivating of the license keys, it will automatically detect those from the machine.
A webpage with more details on this is: http://www.tableausoftware.com/community/support/kb/upgrading-tableau-server