Hello.

Yes you can leave the seat and grab the one that you prefer more. But every college has it's own different rules and policies. It's better to talk to the admission or management department of your college as soon as possible and get your doubts cleared about the process of withdrawing your admission. They might ask for valid reason with proof or some compensation money that they will cut off from your admission fee. Your main enquiry should be about the return of the original documents and the fee paid that is to be withdrawn. But it is totally possible to change college if you want. So go for it.