UPDATE: Noopl 2.0 removes the need for acoustic coupling as audio is transferred to the iPhone via the Lightning connector. Cosmetic spacers are included if you'd like to fill any gap between the top of the Noopl device and bottom of your iPhone.
To change a coupler or spacer, gently pull up from one side and then repeat on the other side. There are small pegs that keep them in place.
Reverse the process to install the new one. You'll feel the pegs snap into place when properly inserted into your Noopl device.