If this is regarding 50% All India Counselling, let's say you opted for upgradation of seat after Round 1 and you have been allotted a seat in Round 2. You can exit the seat by forfeiting the Tution fees within 2 days of publishing the Round 2 results. This means that if you do not want to go and  join the seat, you will have to let go off the Tution fees. Here the tution fees is the security deposit that you must have paid for registration for the Counselling process of 50% seats at All India Counselling. And you have only 2 days of time to take a call on this. Now if you  have joined the College allotted in the Round 2, then you cannot resign or cancel the seat. So in other words, from the time you have been allotted a seat and for you to decide whether you want to retain it or not, you have 2 days. But again this is also subjective to the Eligibility. Please go the tough the FAQs for more clarity on this. You can check the FAQs and the flowchart for the Counselling process from the official website: https://mcc.nic.in/PGCounselling/Documents/mergedFAQs.pdf