I've got several wallpapers 1920x1080, 2048×1080 resolution, as well as smaller pictures that I want to make suitable (i.e. quality, resolution, etc) to be printed into A0 posters.
I have access to Adobe image manipulation products if that's necessary.
How do I go about that?
Well, I guess Google can help.
Yes, I might've overdone it a bit. But I'm happy with it to print on an A3/A2 poster. I'm not entirely satisfied how the eye came out, but I can only do so much with Illustrator. I'm no graphic designer.