H1 to F1 if I-140 is approved

[usavisainfo69]

I am currently on H1B visa, I filled for Green card in EB3 category priority date Dec 2010 and my I-140 is approved. Recently, I got admission for pursuing a Full-time MBA in a good university. I read in few blogs that my chances are very less to change my status to student visa (F1) if I-140 is approved. Is this correct? Please suggest me how I should proceed in this situation.

Thank you!