Some photo editing programs can easily enlarge an image, and increase pixel count to avoid a 'tiling' effect. But an easy way is to enlarge the image to about 8x desired, then use the "sharpen" effect. May take a few seconds to effect the change.. then shrink the image to desired size. It should have good detail. But if an image is only 400X500 to begin with, you cannot add detail that isn't there. Best to start with a hi-res image.
An image that was resolved for 640x480 seen on a screen at double that image size will always appear 'tiled' or coarse.
To get a crisp base image, you need a camera that has at least a 4 mp resolution. Cell-phone and Web cams are lucky to have a 1 mp resolution.
F@H.. to solve mankind's maladies.. in our lifetimes!