This is not an automatic process as on some other printers, some menu steps are required prior to physical replacement.
If you try to just insert it on your own you can actually damage the printer.
It must be initiated via the menu instead.
Press the home (house icon) button and select Setup (wrench icon) > Maintenance > Ink Cartridge Replacement.
Lift up the scanner unit (below the glass)
Open the cartridge cover
Squeeze the tab on the cartridge and lift the cartridge straight up to remove it.
Gently shake the new cartridge four or five times, then remove the cartridge from the package, removing the yellow tape.
Insert the new cartridge into the holder and push it down until it clicks into place.
Close the cartridge cover and push it down until it clicks into place.
Select Check on the LCD screen to make sure the cartridge or cartridges are installed correctly.
Close the scanner unit.