Hi Fred welcome to the board
There will probably be more to it than just changing the extension depending on how your system is set up. It may be easier for you to just change the two physical locations of the phones via the cross connect and re-assign the two extension numbers. In order to set up another phone to be a 2nd attendant you may have to program several things.
Do you have a manual or CD documentation for the system? If so, it should provide the information you need.
We try to freely provide information to the end user with information regarding simple questions that can easily be found within the user guide. We also provide and exchange information with other Telecommunications business owners and professional Telecommunications field technicians. The programming that your system requires would involve in depth installer level programming.
Do you have a vendor that you could call to assist you with these changes? If you would like, you can check out the link at the top of the page labeled "Installers". Search around your area and you can probably find someone nearby to come to your site and make the changes for you.
Goodluck
:thumb: