From the xCenta Dashboard, click on Tools > Admin in the top right of the screen.
A new screen will appear. From the Administration screen, click on Manage Users.
On the Manage Users screen, select the appropriate user by clicking on the 
icon on the right hand side of the screen.
A new window will appear, for the selected user. Click in the Username field and edit the username as necessary, then click Save.
If you try changing a Username to a name which already exists on the system, a pop up will appear at the bottom of the screen and it will not save the User details.
If you are unable to follow these instructions, you may not have the required user permissions. Please contact your Site Administrator.