Hello Anjali, 

As you have not mentioned the examination in which you want to add more colleges in the previous list with increasing counselling round. I guess you might be talking about Josaa counselling as your interest is in engineering. In Josaa counselling, you can neither edit your preferences, nor you can add or remove any college in the existing list. You can only either freeze, float or slide as per the norms of Josaa on seat allotment.

Hope it helped.!!!