As of Mendix 6.3.0, the version selector detects Modelers installed in different locations because it uses the registry to find out where they are. If you install the latest Mendix version, you will get this new version selector. There is only one version selector system wide, so it will also work for all other Mendix versions. From the release notes:
The Mendix Version Selector now also detects Mendix Modeler versions that are installed in a non-default location. The default locations are (normally) C:\Program Files andC:\Program Files (x86), so if you install Mendix Modeler versions in a different location, those versions are now automatically detected as well.
And there is another feature in there as well:
The Mendix Version Selector now features an 'Uninstall' button that allows you to directly uninstall one or more Mendix Modeler versions.