As usual, Rainmeter 2.2 is fully backwards compatible with skins written for any version of Rainmeter
You need only install on top of your existing installation.
No need to uninstall 2.1 or worry about overwriting changes you have made.
A belated congratulations to our developers on another successful release. I've been absentee for most of the last 10 weeks or so, and it kills me to have missed a Rainmeter milestone like 2.2. But the strength of our team and our community continues to astound me. I can't wait to be back. :)