When exactly did the Great War get a name change to World War 2?

First of all, the name of the "Great War" was changed to World War I.  After the war, it was generally referred to as "the World War," especially in the United States.  When the next big war began, and especially in the 1940's, when the United States got involved, the new war was called World War II, and the previously one was called World War I, to distinguish them in the history books.

It was when there was going to be another one. The Americans were late for the first world war and dilly-dallied about the second to see who was winning but when they saw the Brits were beating the Germans they decided to join in. If it wasn't for the Japanese attacking Pearl Harbor they'd have left the British to beat the Nazis and their Concentration Camps alone.

After WWII it became easier because it was the second time that the Americans had to save Britain's bacon. There was nothing great about Britain's performance in either conflict. 

the Great War was To hard to remember for Americans WW1 and WW2 was easier and the Numbers enabled the Uneducated to Know Which was which

It didn't.  The 'Great War' was the name given to WW I.  Time Magazine coined the term 'World War I' in its issue of June 12, 1939, and in the same issue, first spoke of 'World War II' in expectation of the coming worldwide conflict. The first actual reference to 'WW II' came in the September 11, 1939 issue of Time.

i would call no war GREAT.... people die in those, so its really appropriate and moral to not glorify such things. I think its good they changed it :)

The name The Great War was given to the 1014-1918 war.

Once it was clear in the early 1940s that then ongoing war was even larger than the 1014-1918 war, the ongoing war got the name World War 2, and The Great War got the name World War 1 retroactively.

Shortly after the War of 1812. Otherwise known as the American Civil War. 

"The Great War" is World War One.  But if you're asking about the etymology of the name "World War Two" then I believe the first reference to it in print was in 1940. 

Someone comprehended the projections!