For Linux distributions updates can be obtained using the operating systems standard package manager (if the latest version is not installed automatically you can instead compile the source code). This forum thread and this forum thread may also be helpful to you with installing Wireshark on your Linux based system. For Mac OS X and Windows, the update is available within the downloads section of the Wireshark website. In addition, a detailed FAQ for Wireshark is available here.
If you use Wireshark, please install the appropriate update when you can. If Wireshark is installed on a critical production system or systems that contain your critical data, please back up your data before installing this update in order to prevent data loss in the rare event that an update causes unexpected issues.