Hello Aspirant! If you're allotted a seat in a particular college, you'll be given three options to chose from that will be: Float, Freeze and Slide. If you want the seat but is not satisfied with the branch and think that it can be upgraded according to your rank then you can chose the float option for which you need to pay the seat allotment fee of Rs.35000 with which you can participate in the further rounds and can upgrade your branch or else can continue with the current seat. This fee will be added to the college fees and it's mandatory to pay if you choose the float or freeze option. If you don't want the seat then you can opt for slide option with which your current seat allotted would be lost and you'll be able to participate in further rounds.
Hope this helps.