So is it true that i can change ss to ß and vice versa? thanks for your answers!!!
Words like Waßer, wißen etc would simply be wrong. The ß is only used if a "sharp" (English) s follows a long vowel or a diphtong, like in weiß, außer, ließ, schießen, aßen etc. An "ss" can be used as a replacement if "ß" is not available and it's even the standard in Swiss German.
PS: There's a joke about this: "Der Arzt hat gesagt ich soll Bier in Massen geniessen". Here the replacement just reverts the entire meaning....