NOTE: If you need to change your password, make sure to first change it from cPanel (click here for a guide)
Step 1 - Click Settings
Then Click Accounts & Passwords
Step 2 - Select the email account you want to update the password for
Step 3 - Update the password under the Incomming Mail Server
Then click DONE at the top of the page. If you get an error just enter your new password again and make sure it's correct.
Step 4 - Go back into the email account
Then click on SMTP
Now select the Primary Server
Step 5 - (1) update your password and (2) click Done. If you get an error just enter your new password again and make sure it's correct.