To deactivate a user account you must navigate to Admin-->User Management.
User Management is where you can see create/deactivate users, see active users, edit user preferences, change user types, as well as changing usernames and passwords:
The very far right icon is the deactivate user icon. After clicking on it the following window will appear:
After clicking 'Select Employee' when changing ownership of records you will get the following pop-up window to select an internal employee to move the record ownership to:
Note: If you utilize AkkenCloud as your email client you can also move existing and new emails that were originally tied to a user and move them to another user(as long as they have an email account configured in AkkenCloud).