You simply uninstall the Lightroom you are using now. Sign up for the creative cloud and install both Lightroom and Photoshop from the creative cloud application manager. Once you have done that you can simply start Lightroom normally. It will open the catalog that you have been using and you will be able to pick up right where you left off. You really do need to uninstall your standalone Lightroom. Installing it from the creative cloud manager installs the exact same program, but it is licensed differently. The transition is very smooth. At least it was for me.