Are you trying to detach the speaker base or the speaker from the monitor?
Usually, you need to slide the speaker upward to detach it from the monitor but look for a pin, knob or a lever for locking mechanism.
To remove the attachment from the speaker/s; check for locking mechanism like pin, plastic tab etc. some of them you need to push or pry the tab a little so you can slide the base and speaker apart.
If my direction isn't clear enough, take some detailed pictures on your unit and post it back here if possible so we can help you further more.