You can edit your username any time you wish from your dashboard. Here is how:
Login to dashboard and click on the drop down next to your profile image. Now click on Settings.
Account Settings: Here you can change the mobile number,password and the username.
To change your username, click on "Change" like shown in the image above.
You can edit the username and check the availability.
If the username is available click on "Change Username" (Refer to the Image above)
Note: Changing your username will affect your payment flow on your website/app and other places where you might have shared your payment and product links. It is advisable to replace them with the new username.
If you are sure about changing your username, click on "I Understand, Change my username". Your username will be updated successfully and you will see the message as shown in the image below: