Following instructions cover the steps involved with changing the password in your Web Hosting powered by Plesk. If you need to change the password for a Professional or Classic Hosting email please read How do I change my email password? - Professional Email and Classic Hosting
If you need to change a password without access to the Rebel account, please follow the steps here.
Login to your Rebel account and click Hosting Manager.
Click the green button that reads Control Panel. This will open the Plesk Hosting OS in a new tab.
Go to Mail.
Click on email account you would like to change password for.
Specify a password consisting of fine or more Latin characters. Make sure to include a mix of upper and lowercase letters, numbers, and symbols to create a strong password.