Anti-Malware clients managed from the Management Console are updated from the console itself.
When a new Management Console version is released, it may contain an updated MBAM client.
To update your existing clients you must perform a client push install over the top of the existing clients. (Instructions here.)
Alternatively, you can export an updated client package from an updated console, then use that for a manual upgrade on the client. (Instructions for exporting a client package here.)