Can the stand in a Mid-2011 21.5" iMac be removed?
iFixIt.com have some of the best step-by-step guides for repairs on just about any Apple device.

I found their guide for removing the stand of your iMac here:
https://www.ifixit.com/Guide/iMac+Intel+21.5-Inch+EMC+2389+Stand+Replacement/113471

I see it as a little bonus that it's based on steps - that way you don't have to pause the video multiple times.

Good luck!