Is there anyway to stop a download on Steam?
Solution 1:
In your library list, right click on the game you wish to cancel the download for and click 'Delete Local Content'. This will remove the data that has already been downloaded and remove the game from the download list.
Solution 2:
This solution works for every game on Steam:
Go to your library, right click on the game you're downloading and want to remove and select "Delete local content". That's all. You don't need to stop or restart Steam this way.