To change your password:
Click on Settings > Profile > Security. Then just enter your new password (twice, for confirmation).
If your Superchat account is associated with a Google account, you will need to change your password directly in your Google account.
How to reset your password if you have forgotten it:
Go to the Superchat login and click Forgot Password.
Enter your email address and click Continue.
After that, you will receive an email with a link to set a new password. This may take a few minutes and can sometimes end up in your spam folder, so always best to check there just in case.
Once you have reset your password, go back to the login page and enter your new details.