It doesn't look like the renderer is working right now, so at the moment, you can't. But if it were working, here's what you would do:
1. Go to the comic's page, e.g. http:/[i][/i]/www.stripcreator.com/comics/markgwret/580647.
2. Look for the yellow box under the comic.
3. Click the link that says "make png".
4. Your operating system should take over from there.
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The what mentioned above is total fiction. Please don't take it seriously!