The B-2 Visa extension is an application that you file with USCIS requesting an extension of your B-2 visa status.
You can generally request up to 6 months at a time.
You use USCIS Form I-539 to request your B-2 Visa Extension.
You use USCIS Form I-539A for each family member in B-2 status applying with you.
The USCIS Filing Fee for the B-2 Visa Extension is $370 plus $85 per applicant for the Biometrics fee.
You can apply as many times as you like, but USCIS determines each request in it’s own merit.