I have a Canon iP4000 which I converted into a direct printing on disc using the instructions on Damn Printer website. It works perfectly fine except I recently got a message that my printhead should be replaced.
I opted to get a new print head through Canon and got it and the box says it is for the iP4000 part QY6-0049.
I am a comparative newbie and (1) there was no instructions as to how to install a new printhead and (2) eyeballing the part and the printhead in the machine - it does not look like the printhead in the machine.
Vintage48 was right, canon usually have their instruction for that or refer to your owners manual.
But in anycase there should be two lever: 1 for replacing ink tanks and one for the whole head unit.
Make sure you wear surgecal gloves and just incase lay garbage bag on your working area, you don't want unwanted inks every where. And remove ink tanks after printer head has been replace to avoid spills.