In order to change the password of an email account in your SWPanel you must follow these steps.
Log in to SWPanel and go to the Dashboard of the service where the email account to change its password is located, using the search engine located at the top of the page.
Once inside the Dashboard of the service, you must go to. Service Management → Mail Management from the blue side menu.
Click on the three dots [...] on the right side of your email account and click on Modify this email account.
Type in your new password or generate a random one. Finally, click on the green Save changes button at the bottom of the page.