dear aspirant,

Now you have kept that seat in your choice list and if you got that in first round then go for registration for reporting at your nearest center with all the documents which is required(list of document is available on website of JoSAA) but take care to mark for Float option if you want seat of higher preference in any college of that choice list or Slide if you want a seat in same college but other branch. But you will get other seat only if you have some other choice with higher preference. Then in the subsequent round if your rank is enough then you will get seat which is at higher preference in your choice list. If you get seat until sixth round is not the seat you want to take then you can withdraw from the process and the fee which you have paid via DD will be refunded.

hope it helped