Change youtube name - how?

Your handle is a separate thing from the channel name. Changing the name leaves your @ and channel URL alone; changing the handle changes the URL, so old links to it stop working. Also, if the channel has the verified tick, renaming it loses the tick and you'd have to apply again.

Studio, then Customisation, then Basic info. Change it there and save. Two things people don't expect: renaming the channel doesn't rename your Google account any more, they were split apart a while back, and there's a cap on how often you can change it inside a short window, so don't sit there trying five variations to see which looks best. Your existing videos pick up the new name on their own.