If I have enrolled in counselling in 2012 and not got desired branch, hence would like to go for 2013 jee.

Is it possible?

In the brochure it was written to register for the course then withdraw to be eligible. But is there a way without enrolling?

yes it is possible if you have not paid your registration fees. 

DEAR KAUSHIK

first tell me your JEE 2012 rank.

My AIR is 7194.

I have not got any branch in the 2nd round of counselling and now I want to withdraw my name from the 3rd round.What is the procedure?

I would like to be eligible for JEE2013 too as this was my first attempt.

u need not withdraw from the 3rd counselling because even if u are alloted a seat not of ur choice, then u are absolutely eligible to give iit next year if u dont pay the registration fees.....if u lyk my reply, dont forget to approve it....