Don't know about Lightroom, but the Photoshop you want to deactivate first (Help/deactivate). Then in OS control panel use uninstall feature.
Unless you really need the space it is best to leave sleeping dogs lie. Some users run into file association problems when uninstalling a previous version of PS.
Is it recommended to do?
It's not recommended nor is it not recomemnded. It's entirely your own decision. As Curt said, there are certain side effects, in addition to file associations also shared components possibly breaking down (PDF libraries), so if it's not that critical, leave them in place. otehrwise you may have to reinstall CS6 after you have removed the other versions.