can i apply for a student visa although i'm in the u.s. with an b-2 visa?

Answer 1

Yes, you can.

Whether Immigration will allow change of visa or not is a separate question- it is up to the US CIS to allow such transfer. You might be asked to return to home country to apply for student visa. At the very least you have the burden of proving your change of intent.

Answer 2

You file Form I-539, Application to Extend/Change Nonimmigrant Status with required supporting documents and fee. You need to apply and get F-1 visa stamped with the approval of the petition at the embassy, when you go out of US to come back.