If you forget your password, go to the login page of the phone app or web app, and click ‘Forgot your Password?'. 

Enter your email here to be sent a new password setting link. 

To change your password while already logged in: 

1.  Head to the web app
2. Click on your name / account name at the top of the menu bar
   
3. Go to 'Profile settings'
   
4. Here you can edit your name, email address, or change your password (top right corner of the screen).