Sabata:
While you were under the F-1 visa, you were exempt from Social Security and Medicare taxes (provided you did not exceed five calendar years in the U.S. under the F-1 visa).
If the Social Security and Medicare taxes were withheld during your F-1 visa, you need first to ask your employer to refund to you. If they refuse (most likely), you must get the refusal in writing (be nice, but insistent).
Once you have the written refusal, download IRS Pub 519 from
www.irs.gov and read pages 44-47. It goes over the procedures for requesting a refund. You may or may not get it; it is
NOT automatic. However, it costs you nothing but a little time and some postage to ask. There s no penalty if they deny your request.