Endpoint Protection 12 Client Auto Update

So I've finished upgrading the Endpoint Manager to Version 12.1.5

I have added the installation package for the 12.1 client to the client group in the Clients section.

Am I right in thinking that when the client checks in, it should pick up the new client and install it?

So far, none of my clients have picked it up, I've even done an update content command on them and have confirmed that they have picked up the latest virus definitions, but they still have version 11 of the client.

Is there something more than adding the installation package to the client group that you need to do to get the clients to update?