You need to download Impulse. Patching for Sins of a Solar Empire is through Impulse, somewhat similar to how Valve patches their games through Steam.
Impulse will patch Sins to v1.191, the current (IIRC) version. You'll also be able to acquire the Entrenchment, Diplomacy, and even the upcoming Rebellion expansion through the service, should you choose to purchase (or preorder, in the case of Rebellion) the expansions.
