Alternatively, you can click on 'View mod in workshop' (the button with the Steam icon) and unsubscribe from the Workshop itself. If you subscribed to a mod from the Steam Workshop, you can uninstall it from within the game: Instructions for uninstalling mods from the Steam Workshop:

Make sure it is checked / enabled after it finishes downloading.You might see a download progress bar in the list item if it takes a while to download. Return to the game, and you should see the mod listed in the Workshop mods list. Browse items in the workshop, and when you see a mod that you like, click on the 'Subscribe' button. The Steam overlay will open and show the Workshop.You should see a 'Browse Steam Workshop' button on top of the second list.Run the game while Steam is running, and open the Mods menu from the main menu.Instructions for installing mods through the Steam Workshop: