Dear Student,

If you are already registered then you don't need to register again for the further rounds.If you have not registered  previously in any round then you have to register and have to pay the registration fees as you will be considered fresh candidate.You can choose float option if you are not satisfied with the seat allotted to you in 1st round.You can read more here

https://engineering.careers360.com/articles/upsee-counselling