Usernames are only used to log into your Ashley Madison account. Other members cannot see your username. Your username can only be changed on the Ashley Madison app.
A nickname is a screen name visible to other members, and can only be changed on the desktop or mobile Ashley Madison website.
Regardless of whether you change your nickname, your username remains the same.
To change your nickname, log into your account on AshleyMadison.com and follow these steps:
Desktop and mobile web
Click on Profile;
Then on Edit (beside your nickname);
Update your nickname; and
To change your username (login ID), log into your account on the Ashley Madison app and follow these steps:
Tap on the three pink horizontal lines [☰] in the top-left corner;
Then on Settings;
Then Account Information or Account;
Type in your new username; and
All text changes must be manually approved by an administrator. Additions or changes are usually approved within four (4) hours, but can take up to 24 hours during peak times, weekends, and statutory holidays.