If you want to start from the scratch, then it is the best, if you uninstall the old version before installing the new one. But this always will delete all data concerning the component. Meaning your settings, the user relations, offline messages, in future the stored profile, etc...
If you just want to upgrade an existing installation of the component, then you should NOT uninstall the old version first to keep your current data in the database.
Greetz
FoTo50