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://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.
The what mentioned above is total fiction. Please don't take it seriously!