No need to uninstall anything just reinstall DAZ|Studio over the top of the existing program and click on "yes" when it asks if you want to uninstall the previous version first. One thing you should do first, though, is get the new installers for all your plugins. and remove the old ones. Don't just re-install, there are new installers to be downloaded that will work in v1.2 reset your downloads, and the freebie plugins can be got from the DAZ freebie page as usual.