I want to ask that after first seat allotment. If I want to upgrade my seat then either I have to go to allotted college for registration .
https://engineering.careers360.com/articles/jee-main-counselling-seat-allotment
Visit this link to clear all your doubts regarding .
Visit josaa business rules to get the idea about same.
Yes you have to to alloted reporting center for freeze,slide or float.
https://josaa.nic.in/webinfocms/public/view.aspx?page=46