The installer that you download from the dev center, is somewhat of a "smart install."
It will update from whatever you already have, if you desire a "clean" install, then you need to take extra measures that are listed in other threads on the forum.
If you desire knowledge of that, google LionDiskMaker for Mavericks...
I am assuming though that you want to update/upgrade. If you do it the normal way, of copying the installer into your applications folder, then this means you already have OSX running with another version of OSX...it will just update, normally without issue.