How do you change your display name in yahoo chat?

When i go into a chat room I have a name i didn't set up and i want to change it but don't know how. I looked on yahoo help and it said to change it at the drop down menu when you enter a chat room but it won't let me change anything and it shows a completely different name. How do i get what i want on there?How do you change your display name in yahoo chat?
Click messenger top left in the messenger window. scroll down click my contact details. make your changes, click save and close

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