how do I update on windows?
If you're on mobile, then update from the App Store or Play Store. If you downloaded it from here, you're a FUCKING idiot you should've downloaded it from Steam, but I'll still help you.
Downloading and playing:
Download the .Zip file, right click and click EXRACT ALL. Look in the files you've extracted till you see one with an icon of the red Among Us dude.
Updating:
Re-download the file off this website and delete the previous version.
PS. The reason I said you should've downloaded it off Steam is that it's easy to update and much easier to download.