I only need to know how to try to renegotiate my Merit offer.

Renegotiating a merit offer depends a lot more on the colleges you've gotten into than your stats or grades. Colleges will typically give more merit aid out when they see that you've received a better/stronger aid package from another comparable or similar school. You could also ask them to consider you for more aid if you've had a big achievement since applying—like a big award or competition victory. In either case, you should write to or call the admissions office and ask them if you can be considered for additional merit funding.

I also believe the name of your high school was removed from your post due to the personally identifying potential of that name + your username. In the future, please do not include any personally identifying information in any post on these forums.