Ive got a hp printer with a photo tray for 5 x 7 inch photo-paper, how do i get my computer to print on it?

It doesn't tell me in the manufactures guide, or the part that I have anyway. Its a C5280 hp printer.. its fine to print on a4 paper but i don't know how to get regular sized photos to print out. I have plenty of paper in there. thanksIve got a hp printer with a photo tray for 5 x 7 inch photo-paper, how do i get my computer to print on it?
Follow the guidance/instructions offered on this page of the HP website.

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