Yes you can, but pay attention to the important notice on the change username interface.
When you change your username, it also changes your affiliate ID. When you change your affiliate ID, you cannot use the old affiliate link and all your existing affiliate links on the web or waiting to be clicked will stop working!
Change your username at your own risk and with caution.
To change your username, click your profile picture top right of site.
Select the settings option.
Click manage username and follow the instructions.
Click the MY STATUS button on your dashboard and then click - Manage Username.