Completely reinstalling may not be necessary. I had the same question as you and found this on another website:
"To be able to "reset" the GMAT Prep software, you do not have to uninstall the software. Please do the following:
1. Go to C:\Program Files\GMATPrep\Exams
2. Within the Exams folder, you should see a Practice Test 1.log and a Practice Test 2.log
3. Delete both logs
4. relaunch the GMAT Prep software, and it should show you that both practice exams are now Not Attempted, and you can take them again.
The database for the GMAT Prep is not currently very large, so you might see several questions that you had taken previously.
Hope that helps!"
Hopefully that works on your end. I did it this weekend and it seemed to do the trick.