If you are using the default settings in 1.2.0.9, and all of your process configs are the same, you should uninstall 1.2.0.9, restart, install 1.2.1.0, restart, and go from there.
if you have special instructions and different processes set up, i'm not sure if they will be saved. try upgrading without uninstalling, then if that doesn't work write down all of your special configs you made and do it the way i said first.
i always do a fresh install, but i don't have mine doing anything different then the default settings.