Hi David. Welcome to justanswer.
Do you have the new cartridges with you?
If yes, then turn on the printer and open the paper output tray.
Now lift the Scanning Unit (Cover), then hold it open with the blue coloured Scanning Unit Support
Did the cartridges move to center?
Once you click this link below on your computer(CLICK HERE)A file will automatically get downloaded. Check your download section, a file named ELSINORE.SCREENCONNECT will be present. Just open that file so that I can connect to your computer.
Check this gif that will guide you how you have to remove the cartridges
Prepare the new FINE Cartridge. Take a new FINE Cartridge out of its package. Remove the orange protective tape gently https://support.usa.canon.com/library/attachments/ServiceWareImages/LDImages/WSSS/NewWSSSImages/G0082961.gif
Lift the Scanning Unit (Cover) slightly to set the Scanning Unit Support back to its original position, and gently close the Scanning Unit (Cover).