itch.io

If you want to update read this

For mobile, go to google play or app store and search among us click update

For PC, and itch.io, it will automatically updates

Now for steam, 

you have to:

1. Launch Steam and head over to your library.
2. On the left side-bar, right-click on the Among Us icon.
3. Select properties from the list that appears.
4. Click on beta.
5. Select public beta. And then click on close. The game should update automatically after that.

hope it helped