Many Confuse Between the login name (login ID or User ID) and the name displaying over the posts,

But the fact is that both are different, the login name (login ID or user ID) is the fixed name generated by the system 

and the display name or user name that is displayed over your post can be changed.

To change, after logging in

Click User Menu in the main tab and click on Settings and you will see a settings page where change the username at Your name and after entering your Desired name click save.

Refresh Techie and after that all your early posts get changed to your new name..