I would just keep it as a UW. It will probably count as an F as I would assume that, like in the case of most schools, unoffical whithdrawals count as a 0.0 with the full credit hours. It is possible however that, like the community college I went to, your institution counts a UW as a W - not affecting your grade. In this case, it appears that it would possibly be treated as a W by AMCAS as vaugely stated here in this quote from the AMCAS instructions:
Grades of "IF" or unauthorized/unofficial/administrative withdrawal may be treated as "F" in
the GPA depending on how they are considered by your school.
You should contact AMCAS about this after finding out how your school calculates UWs. In either result, why change from a UW to an F? After all, assuming that the grades are equivillent (hopefully not), why go through additional effort to get it changed when it will make no difference as far as AMCAS is concerned. Another argument would be based on intuition. We see F as the worst possible grade. Even if numerically equal, F just looks nastier than the UW (weak, I know, but hey.) Good luck.