Most digital cameras store images as jpeg files so you shouldn't need to change anything. If your photo is in a format other than jpeg you will need to convert it before uploading to our site.
Converting your photo to jpeg953x953 pixels is the least amount of pixels needed to print our smallest product (400mm x 400mm) at an acceptable quality. The amount of pixels in your photo is dependant on your camera settings - a higher setting means more pixels. Any digital camera purchased in the last few years would easily reach these requirments.