Adding mother's name jointly as flat owner

Dear Experts,

I had purchased a flat through loan from IDBI Bank at Kolkata in 2013. Although the loan has been jointly taken by myself & my mother but the flat has been registered in my name only. Now I want to add my mother as co-owner of the flat.

I want to know if it's possible to change the deed as I have a bank loan running. If yes, then what is the procedure & cost involved.