Transfer of property

Hello My parents has a property in Delhi. In that property, of the 2 floors and roof rights that my father owned, he has given one floor to myself, one floor to my sister and roof rights of that floor with her as at that time there was no provision to construct the 4th floor. My father passed away 6 years back. last year my mother wanted to divide the roof rights between me and my sister because of the new law of constructing 4th floor and from the perspective of being fair and both of us were agreeable. However she passed away about 6 months back. We both are still of the same opinion that property should be divided equally between us. How do we go about doing this because will gives roof rights to my sister. Regards Anupama