Can you upgrade 10.1 to 10.2 on single machine?

I am starting down the path of upgrading from 10.1 m040 to 10.2 m020.  So far looking at the the documentation, it looks like I need another machine to install 10.2 on.  What I am trying to do is to install it on the same server that I currently have.  I know that is how I did it with the 10.0 to 10.1 upgrade, but I do not even get the Update Existing Installation button.  Do I have to have another machine or is there a way to do it on just one machine?  If I can do it on one machine, does anyone have a simple outline of the steps that are needed?

Thank you,

Brian