My dad wants to change his will because he does not want his property to go to the government if he dies first. My mother who is very ill has to go

into a nursing facilty for care eventually. How can he change his will? As it stands now all will property will revert to my mother and the state will take the property when she dies to cover the nursing home fees. He wants my mother to have money each month from the rental property so her needs will be take care of.