So, when do you have to change your password?
For small companies is changing their passwords for about a half a year or a year the minimum.
Larger companies that have to deal with more security, I should say, every month!
If a person's is fired or leaving the company, you never know what their up to do.
If an external company does the IT and server and you are changing or decide to do the IT by yourself, or another company, than make sure that all passwords has been changes before you take over the server.
If you maintain the server and IT of the company and you get fired or decide to leave the company, inform the company to let everyone's password been changed the day you left the company. Why? Because if someone hack into their system than you cannot be blamed for it because you know some passwords of the company, because they changed it. Maybe something to ad in a paper that is been signed by you and the company.