Property will

I am unmarried female. My parents own a flat wherein my mother and me live. The flat is in the name of my father and mother out of which my father had passed away few years back. The property is still now legally transferred in the name of my mother. I have a sister who is married. Now me and my mother wish that the flat should be legally in my name only once my mother passed on. What sort of legal papers should be drawn now that gives the complete ownership of the flat in my name only ( sister cannot claim any right to the flat) ?