You have to click on the "Town" button in the top right (which is partly blocked by the itch buttons. Reaching the named buttons is easy enough, but the settings button requires you control+scroll in the page itself and makes the game misbehave because the ui code handles resolution changes badly), then you can click to upgrade your max automatons!
I'm finding this pretty interesting, so hopefully you're able to give it a shot and see what you think, too!