H1 to B2 to F1

[ToniToneTony]

Hello,

I have a question to ask. I was on a H1-B visa, and I lost my job a few months ago. I put in a change of status to a B2 visa, and my application there is in processing. I did this at the end of September 2017. 

I am thinking about going back to school for a masters in Jan 2018. Does anyone know how this works? Do i need to wait till my B2 is approved before I can change to an F1, or can I apply to change to an F1 as soon as I get admission into a school? How long may this take, and can i be in the country whilst this is happening?

Also, would I have to leave the country at any point? 

Thank you,

Tolu