How can I remotely update my customers game scripts?

Hi, so it looks like asset bundles only store references to scripts, so how would I go about updating my customer's current game code (I figured I could just update the script inside the asset bundles which are served online...seems not).

Would they need to download a completely new build each time or is there another/nicer way?

If not, anyone know of any auto updater script that's readily available? Much like the one Unity itself uses I guess - which auto detects if your version is out of date...

Cheers