Can you explain better what you want to do?

Maybe I can help you but I do not understand what you want to do. 

i show  here. what i want to change

Just tested and no the tab stays showing username not real name so it will be custom coding deal.

Dont forget if you have their real name on the tab, the google spider could add that to google listing. You might want to say something about that in your privacy or TOS so that user are aware their real name could show up on google search.  I dont know if that tab data gets indexed or not.  

I did find something in the seo users page but that is just the display text of $user_name  its not the value as it has not yet been converted yet from var to value.   The lang keys are base+meta_desc_user_page and base+meta_title_user_page

$user_name is a global var so you may have to create a new var called $display_name and then change the value in the lang key or just overwrite the value in the seo php file.

Username is a field that does not support spaces and OxWall does not support duplicate usernames, so they can be part of a profile's URL.

Displayname ... you can have several members with the same real name and even with spaces, so they cannot be used as a profile URL.

If I understood the problem well -Using DisplayName instead of UserName as part of a profile's URL-, it has no solution.