Photo size is determined in pixels and depends on the number of millions of pixels (megapixels) of your camera. Thus, 2-megapixel camera will be able to get a good picture at a maximum resolution of 1600x1200 pixels and print without loss of quality this photo on photo paper 10x15 see the same 24-megapixel camera will have a resolution 5398х3602 and print it in perfect quality on photo paper size 45х30 cm is little more than a sheet of paper of A3, or two A4 sheets.
So the more megapixels in the matrix of your camera, so you have more opportunities to make a great photo, and then print it.
In order to take a picture in the highest resolution possible for your camera, you need the settings to find the section in which you can set the quality of the pictures, and choose the maximum.
After you put the best picture you can take photos and then copy them to a flash drive or disk and take to a photo kiosk where you print large photos.