After first set of seat allotment you will be asked whether you are happy with the alloted branch and the collage or not.
If yes you freeze.
If not you have 2 options…
Slide i.e you can go to a preffered branch of your higher preference in same institute.
Float i.e you can go to a different institution different branch of your higher preference.
And hence the other two round continues. At last if seat is vacant you can avail spot counselling which is conducted by the respective institution. Good luck!
Choose your preference list wisely. Even if you think that you have slim chances of getting in a particular college/university do put it in your list as you never know. There is no option where you can change your preference list in further course of the counselling