Why was Ancient Ireland origanaly called Scotland when and why it changed to Ireland?

This is incorrect. Ancient Ireland was never called Scotland. It was known by various names, including Hibernia, Ēriu, and Banba. The name "Ireland" is derived from the Old English word "Īrland", which is thought to be derived from the Proto-Celtic word "*iweryon", meaning "fertile land". The name "Scotland" is derived from the Latin word "Scotia", which was used to refer to Ireland in the Middle Ages. The name "Scotland" was later applied to the northern part of Great Britain, which was originally known as Caledonia.