You go to Google.com and click Images at the top of the page.
That displays a little form with a small camera icon.
Click the camera icon.
That displays an interface you use to choose a picture on your computer for which you want to search.
Once the picture has uploaded, google displays all the websites that have copies of that picture. There will be a few at the top organized as small/medium/large, but below that is a list of websites - maybe several pages long - where you can get copies of the image at varying sizes, and each listing displays the size of the image available at that site.
What I usually do is download 5 or 6 large versions of an image, then compare them in a viewer app and choose the best one in that group.
In this case, the pic I'll morph is a bit smaller than the one you posted, but it's a much better scan. A clean image - something that looks smooth and clear like a continuous-tone photograph - is preferable over a larger image with blurs, graininess, speckles, blotches, smeared areas, faint block-like patterns, etc.