You can either use the Control Panel in Windows to Add/Remove Software, or you can simply delete the G-Wizard directory from Program Files.
Alternatively, if you run the Installer on the Install Page (Calculator Install, Editor Install), and you already have the latets version, the Installer will tell you, "The same version of the application you opened already exists on this system." It gives you the option to either "Uninstall" or "Run Now". Choose "Uninstall".
G-Wizard keeps its configuration information in separate files. You can delete them, or keep them if you're installing a new version and what it to pick up your old config information. They are located in:
C:\Documents and Settings\<YourNameOnTheComputer, e.g. "BobWarfield">\Application Data
Look for the GWizard directories. There may be more than one if you've ever had multiple versions installed at the same time, but this should be unlikely. The files are updated every time you load G-Wizard, so if you're in doubt about which one it is, load G-Wizard and go see which one has the latest time stamp.