I have never yet encountered an email account that did not have a password.

There is and can be no particular dependency between Thunderbird and an email account. Thunderbird is merely a tool for working with email accounts.

I take it you don't own or have control over the account in question. If you did then you could close it or change its password.

If in fact you don't have access to it nor control over it, then there is nothing you can do.

I say again: Thunderbird, or any other email client, is only a tool to work with email accounts. The account that concerns you exists on whatever server the user got it from, regardless of which email client, Thunderbird or otherwise, he used.

I am the owner of the company and my employee has this email address for our artwork dept and I want to change the password because I don't want him accessing it.

Your mail server/service probably has either a web-based administrative interface or a separate, stand-alone program, for setting up and modifying email accounts. You'll need to use that, you can't make this change through Thunderbird itself.

You need to go to the provider of the email account and change its password there. They will probably have a webpage where you can do this. To change the password or close the account you'll need to know its old (current) password, or be able to demonstrate in some way that you are its rightful owner.

Your domain and MX records are with GoDaddy, so most likely they can help you with this.

Thanks everyone. I figured it out. Thanks for the help