You can install mods by going into the game Options > Game Mods screen. Find the mods that you want and click Install. This will subscribe you to the mod and install the mod into the steam workshops folder.

Once you have installed one or more mods for the game you will need to restart the game. The game will load the mods from the Steam Workshop Installation Path specified in the Settings screen. If your installation path diverges from the one specified on that screen, make sure you update the path in the Settings screen otherwise the game will not find the mods.

Steam doesn't provide an automated way to do that for us, but the game subscribes your Steam account to mods updates. When a new mod is updated you might receive a content update notification from Steam.

Go to the Options > Game Mods screen and find the mods to update. They should have some icon indicating that they need to be updated. Click Install and it will install the update.

Don't forget to restart the game for these changes to take effect.

Go to the Options > Game Mods screen, find the mod you wish to uninstall and click Uninstall. This will unsubscribe you from the mod and delete the mod folder. On you have uninstalled one or more mods, don't forget to restart the game.

Important: Any save file for ongoing crusades that rely on the mods that you uninstalled might not load any more given that the content was removed. So make sure to complete any ongoing crusades before you uninstall the mods.