Your downloads are saved to your computer. The default saving location for Windows is C:\Documents and Settings\your name\Shared. In LW tools > options > saving shows you the location of your saved folder. Unless you've changed the location for saving, your files will be safe if you uninstall, reinstall, upgrade etc. It's when people save to a location within LW's program files or Application Data etc, that they can run into trouble.

You can upgrade to Pro after basic's installed. When you install the Pro version, it will automatically remove your previous LW version.

To upgrade to Pro, go to the LW download page & click on the 'get Pro' button.
Lime Wire » Download LimeWire