Urgent!F2-F1

Is there anybody can tell me if I can change my status from F2 to F1 in the third country now? Such as Mexico?
If I change my status to H4, may I study full time?My hu*****and is in his OPT, if he apply for HIB this April, he will have to stop work from the middle of July till the end of Sep. I wonder if I can begin to study as H4 before Oct 1st. Is there anybody can answer the questions for me? Thanks a lot!