Do I need to uninstall previous versions of SU, when I download a newer version?
No. Each major version installs as a separate program.
So there will be 2 versions on hard drive, eating up hard drive space?
Well, yeah. Unless you uninstall the older version. You asked if you need to unistall the older version and you don’t need to uninstall the older version to install the newer one. You might want to wait to uninstall the previous one until you’re finished moving over to the new version. Make sure when it comes to extensions that you install fresh copies from their sources.