Applications to change to F-1 status may be filed by matriculating international students who are residing in the U.S. in a qualifying nonimmigrant status. All other students must apply for a visa stamp abroad
Applicants for change of status should not travel abroad after their application is filed.
Matriculating students in F-2, M-2 or B visa status may not begin studies at the University of Idaho until their application to change status is approved. Changes to F-1 from a B visa status are usually not approved unless the visa or I-94 is stamped with “prospective student.” Students visiting the U.S. as Canadian visitors
or on the visa waiver program
are not eligible to change status in the U.S. Students in other nonimmigrant classifications who plan to change to F-1 status to attend the University must apply to do so before beginning their studies.
Applications to change to F-1 status may be submitted to the USCIS up to six months in advance of the start date on Form I-20, but may not be approved by the U.S. Citizenship and Immigration Services (USCIS) until 120 days or fewer before the start date. Any dependent family members who wish to remain in the U.S. in a dependent status must submit applications to change to F-2 status
Here you can find instructions on how to Change to F-1 Status