Changing Office 365 Credentials

I have recently changed office 365 licences.

I was previously using Licence 'A' to use office 365 applications on a Mac. I am no longer at that company and have been removed as a user, so my office applications are telling me there is an 'error' with account. I now have another account which is valid, how do i revalidate Office 365 apps to work with the new account?

I have all current versions of office 365 for mac.