why was the name changed from stellar Lumen to stellar?
Also what has changed between from the old stellar to the new stellar?
Your question as the same my concern. I still confused about some different names on some exchanges such as STR on poloniex and XLM on bittrex. Why different?
The network has always been called "Stellar" and the native coin was called "Stellar". But they wanted to separate the name of the network from the native coin, so they changed the name of the coin to Lumens and retained the name Stellar for the network. I think the name was changed when they introduced the new consensus algo. But I may just be conflating them.
I think one or two exchanges just didn't update the ticker/name to XLM/Lumens and still call them Stellar/STR. Which is unfortunate.