Microsoft did not make it very easy to deactivate a product key for Microsoft Office 2011 for Mac.
This is probably because they also did not put any mechanism in place to stop you from installing your version of Microsoft Office 2011 for Mac on as many computers as you want.
I didn’t even mean to find this out and, after purchasing 5 different copies, I mistakenly used the same serial on 3 different computers and have not received any errors when working in the program simultaneously.
I didn’t want to be in violation of my service agreement with Microsoft so I decided to deactivate the serial from 2 of those 3 computers.
After a great deal of searching with my incredible Google skills I found the only way to deactivate a serial in Microsoft Office 2011 for Mac.
These instructions were taken directly from the Microsoft website so I don’t think there is any easy way to accomplish the same task. The website also has more detailed information if you’re look to completely remove Microsoft Office 2011 for Mac from your system.