Because service accounts cannot log into the Web UI, they cannot change their own password. If the password needs to be changed, a non-service account Admin will need to manually update it through the Web UI. 

Change Password

1. Locate the user on the Users & Groups page and hover over their account.
2. Click Details.
   
   
   
   
3. Select the Profile tab from the left and click Change Password.
   
   
   
   
4. The pop-up dialog will show you what devices are connected to the service account and warn that you'll need to manually update your password within these devices/services. Click Ok.
5. Enter the new password twice and click Ok to finalize the password change.