h4 to f1 h4 extension denied

[desis]

h4 to f1 h4 extension denied

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my h4 extension got denied..
i am planing to file for f1. i graduated from high school in united states. did my high school in united states, currently 2nd year in college my h4 expring this dec.
i applied for h4 extension but got deined, coz i am will be over 21.

any help or suggestion for applying for f1 visa.
like what papers do i need and stuff

thank you.