Does the game update automatically or do I have to download it again?

If you are using the Itch.io App, I believe it does.  Also, you might need to click update on the game when you are in the Library Tab.

 If you got it via browser then you'll have to redownload it. 

Don't quote me though.

Yeah I checked I downloaded via Browser, I don't have any issue with redownloading it though, thanks for replying so fast!