Can i change my user name ?

You can change your user name. I did about a year after I signed up with TER. Use the "Contact Us" link at the bottom of any page. Explain to Admin what you want to do and why.  

 
You can find their reply by clicking on My TER ( the house or home symbol ) at the top of the page and then click on "My Feedback". It will likely take a day or two for them to respond.