Hello Harshita,
If you are dissatisfied with the college you are allotted in the 1st round of counseling conducted by mcc, in that case you have to visit to the college you have been allotted im the given time and have to apply for upgradation.
You have two options, either to freeze the college you have got and the other option is float.
To upgrade your college you have to choose the option of float. But first you have to compulsorily pay the seat allotment fee online and then report to the college you are allotted.
You have to again register for the 2nd round of counseling for upgradation.
I hope this helps.
All the best for the future!!