On the top menu, select Extensions >> Extension Manager
Click on the Manage tab, filter by templates and search for RSLens! and RSTemplate!, select the results and click on Uninstall (the image below only shows results for RSLens!).
If uninstallation was successful, you should see this message:
The installation of any template, component, plugin or module is done strictly using the Joomla! installer, as the above example illustrates.