Change of status B1 to F1

Hi, currently I am in USA. i have got acceptance by CUNY for the Fall semester. But college is unable to do the change of status. they are asking to leave USA and apply for a visa frm original country. My question is if I deferred the acceptance to the spring semester and after getting the acceptance to original country( don’t know when they could send) and apply in the USA through a lawyer. is that possible? how long will take for a change of status?
is there any weblink for the sponsor’s financial ability list i.e. how much amount they need to show?
Also in the meantime can i apply for an extension of the visa. how long time will take for approval.