While it is permissible to change from one status to another from within U.S., it may not always be advisable.
Typically, when someone enters the U.S., supposedly for a short visit (e.g. B-1 or B-2) and then tries to change it to a longer term visa (F-1, L-1, H-1, etc.), USCIS often frowns upon it (and may not grant it), but the consulates invariably frown upon it. My recommendation in most of these cases is to avoid this type of change. If you have already obtained the change, it may be very difficult to procure a visa whenever you need to travel abroad.