WhyNotGradSchool

I accepted admission to school A, gave a down payment of $200.00 and signed their acceptance form, last week. Yesterday morning I get an e-mail from school B, where I'd rather go, saying they might have funding for me. Two professors can support a doctoral student in their lab and to contact them via e-mail. I e-mailed them yesterday to talk about their research and set up a meeting. Can I switch universities without any legal issues? School A is offering partial funding. Not sure if school B will be full or partial. If you need more details please ask, I might be forgetting something.