Many members of this board are advocates of re-installing GMATPrep. Doing this essentially clears your history, and more often then not, you will see many new questions in your retake.

Here's the problem: the GMATPrep question bank is limited, so upon re-install there is a high likelihood that you will see a repeated question from your previous tests. This is a big deal because already being familiar with a problem/solution will skew your final score.

Bottom line: re-installing may be good for practice, but I wouldn't read much into the score. Most likely your score will be skewed a little high.

Good luck!