could I transfer my Visa from F1 to H1 before OPT? Help

I got a master degree in US six years before, then I went back to China just after my graduation. At present I'm registering as a full time student in US, Could I transfer my Visa from F1 to H1 before the beginning of my OPT? Or I still need to get the second master to begin my OPT and transfer my VISA during OPT period?Help! SB told me that I have got a master, I may apply H1 directly, and do not need to wait for the OPT period. Is that true? Thanks a lot!