I have been alloted PGDM Finance for provisional admission at IMT Ghaziabad. Is there any option to change the branch now?

That largely depends on the number of students that are waitlisted for that particular course and whether it was on your preference list or not in your application form. IMT gives about a week to pay the acceptance fee making the whole process very prompt. But you could always mail the admission office about changing your program and adjusting your paid fee towards that course.