Go to https://www.ashleymadison.com/;

Click LOG IN in the top-right; and

Then on Forgot your username or password?, and enter the email address used to register your profile.

Click on the three horizontal pink lines [☰] in the top-left corner;

Then on Settings;

Then Account;

Then Password;

Enter your existing password, new password, then confirm new password; and

Select Save.

Tap on the three horizontal pink lines [☰] in the top-left corner;

Then on Settings;

Then Account Information;

Then Password;

Enter your existing password, new password, then confirm new password; and

Select Change Password.