Instagram automatically saves each photograph as a 612-by-612-pixel, 72 ppi file. This is pretty small, even by iPhone photography standards (the iPhone 4 can capture 2592-by-1936-pixel images). To make a print of an Instagram shot, you should start by increasing the ppi in an image editor. At the recommended 240 ppi, you'll get a sharp 2.5-by-2.5-inch print. If you really want it larger, you can blow the image up to 4-by-4-inches, but that will lower the dpi to 153 ppi. The print will be larger, but it will also appear slightly softer and pixelated. For more on printing iPhone images, read this how-to.