lol. 8 mega pixels doesnt translate to a file size of 8 mega bytes. But I understand how you could get confused.
There are many variables that affect the size of a photo, including mega pixels, photo format, and other stuff. Please explain what you mean when you say that the file size was too small to make better prints. Did you want to print the photo? In which case 8 mega pixels on the iphone is more than enough (there is no setting that I know of to change the image quality on the iphone). If you are not happy with the image quality, there is not much more you can do other than improving your photo subject. The lens of a camera is as important as the mega pixels (in my opinion) and there is no comparing the lens on a phone to the lens on a camera designed to take photos.
Reply back and we will learn more. In the meantime you might want to investigate camera app alternatives, like 'camera +' for example, or many others.
Vic