Please see this infographic for the difference between your display name and your @username.
To change your @username, please visit http://rec.net. Log into your account and navigate to your profile by clicking your profile picture on the top right.
Find the settings cog icon to go into your account settings.
Once you have done that, in this page you will be able to change your @username and nickname/display name. While you can change your nickname or the name that people see above your face up to 3 times a week, you can only change your @username once. Please choose wisely. We will not be able to change your @username if you have already changed it once.