Yes i understand your query, 

If you are alloted with the aeat in iit after Jossa counselling round1 and you dont want to get that seat confirmed you can cancel the seat allotment by Not paying the fees or any further process

You can select the iit you want in next round and see that you get your required seat or not in iit you want.  But there would be chance Tgat the seat you are alloted would be full if in next round same seat is alloted to other. 

So wait for next round if you want to get admission in iit you wish.