To change your email password login to Siteground.

You will either have to use the OLD cPanel method if this appears when you login to Siteground or the NEW webmail app

Cpanel Method Instructions

https://www.siteground.com/tutorials/cpanel/email/change-password/

New Webmail App Instructions

https://www.siteground.com/blog/new-webmail-app-to-manage-email-settings/

Then you need to update your password on your devices to match what you have set on the Siteground server.