Hey, sorry for late reply!
You actually don't need that much of a PC to play it. I'm also still optimizing the the game so with each new update the game should run better and better, at least that's the idea. The only need I know of is 4gb Ram.
And yes, all you need to do is download the latest full build and you have all content available. It's preferable to do it manually from one of the sites, but if Itch.io app also allows that, you can do it through there. It's always better to download the full build than 'just update' because the engine I'm working on is not really designed to have small updates. Thank you for enjoying the game!