do i need f1 visa stamping again.

Hi,
I came here as a f1 student then i changed on f2(in my wife’s university) now i applied for COS again for f1 in same university . my visa stamp (f1) still valid till 2014(old one) but my i20 changed (paid sevis)so do i need obtain new visa stamp if i will go out of united states and reenter. help needed.

Thank you.