"Clash of Clans" updates are available at the Apple App Store and Google Play, and the game automatically updates to the latest version upon launch. Game developer Supercell recommends checking the official "Clash of Clans" page on Facebook for information on upcoming updates.
Supercell uses updates to add necessary fixes and new features to "Clash of Clans." Game fixes typically involve security tweaks and adjustments to costs and training times for troops and spells. New features generally involve troops and buildings with new mechanics. For instance, the July 2015 update introduced the Dark Spell Factory, giving players three more spells.
Due to the nature of the game, all players must update to the latest version available before they can play. Players cannot revert to an old version, even if they don't like the changes made by an update. Battles that happened prior to an update no longer become available for replay once the update is in effect. In addition to Supercell's Facebook page, news about the latest updates are available at Supercell Support.
For consideration in future updates, the game developers may listen to feedback that users post in the official game forum. Alternatively, players can use the support tools inside the game to send screen captures and feedback.