No, it is not possible to retake a course for a better grade.   Even if you take a course Pass/Fail or R, you may not retake it for a letter grade. 

The Grade of F is the only exception to this rule and it only happens when academic integrity is not involved. 

From GSAS:  To receive permission to retake a course, the student must submit the Registration Adjustment Form to the GSAS Office of Student Affairs, requesting that the course be added to the student’s registration the next time it is offered. Please note: This appeal must be filed no later than ten days after the grade has been posted on SSOL. 

NOTE:  The original “F” will remain on the transcript and will affect the cumulative GPA that is visible on the transcript.  However, the “F” grade will not be calculated into GPA that will determine graduation.