How to change my yahoo birth day date ? I want solution.?

You can't. Avatars and the editing of nicknames, birthdates and other information were disabled more than a year ago. They are making changes to profiles. No one knows when or if they will be enabled again.

It's just called birth date, just because you are on yahoo, don't mean that you call everything yahoo. Also it is impossible to change your birthdate.

dont do it