You can use both of them with the meaning of "manera". You can always change "manera" by "forma", however sometimes you can't do the opposite when "forma" is using in other sense: Example1 : Esto no son formas de comportarse! = Estos no son maneras de comportarse. ("forma" is using like "manera") Example2: No me gusta la forma de esa escultura. No me gusta la manera de esa escultura. (They are not the same. The last one is wrong because in this case "forma=shape which is different to the meaning from "manera")