After installing the new paper tray on the printer. (Presumably, while the printer is turned off.) turn the printer on, then go to the Mac System preferences and select the "Printers & Scanners" icon. Next find your printer on the list of installed devices, and select it. Then select "Options & Supplies..."
When the sub-window opens, the top should have 3 tabs, "General, Options, and Supply Levels". Select "options." A new sub-window should appear.
On the "options" sub-window, you should be able to adjust the number of "optional lower trays" (or similar language for your particular printer). While this window is open, double check that the other configuration items are correctly shown (typically, memory configuration, feature set, etc.)
Once everythign is as you wish, click OK and then close the System Preferences window. The printer dialogs should then reflect how the printer is set up.
I am not sure what the dialogue box would show. I assume the install will be similar to THIS. I would think after power on, it would have the tray show up as an option, or at most you may need to reinstall the driver after tray install. Best thing would be to speak to Support: 1-800-821-2797.
I own a Workcentre 6515 and I am about to buy the extra paper tray that goes under the printer.
My question is: will I be able to select the paper tray from a Mac dialogue box? I checked on the manual but I found no mention about this.
Many many thanks in advance
Greetings from Italy