For most players, the update happens automatically through the Steam Client. If you are using a non-Steam version or need to manually verify your version:
The 3.3.3 update was a targeted hotfix with specific technical goals rather than a content expansion: Resolved a potential security issue. ck2+333+download+upd
Use the "Verify Integrity of Game Files" option under Local Files to force an update if your version number (found in the main menu) is not 3.3.3 (Checksum: SOHY) . For most players, the update happens automatically through