You can change your password from the settings menu on both desktop and mobile.
In order to change your password, you must re-confirm your current password.
If you do not know your current password, you may be able to reset your password if you associated an email address with your account. Without this, there is no way to regain access to your account.
If you are still logged in but do not know your password and do not have an email address associated, we may be able to help you.