Speedo cable disconnection

Guys, I need to disconnect the speedo cable where it comes through the bulkhead and into the engine bay.
There is a round connector, which I can reach up to, but I don't know the technique to unlock the 2 halves.
Has anyone disconnected this before, and if so how does it disconnect/unlock?

Or any suggestions ... ... ...

Pull it ....you need to hold both halves

Thanks Lee, I need to get more ancillaries off, to get closer to it then.