I am not sure myself as I disconnected that brake light, as spoiler has third light. I will see what I can did up for you in the mean time. I can find every light except the HMSL (High mounted stop lamp) on the KGIS site.
I just did this.. There's the black cable clipped into a grey plastic bulb holder... I unclipped the wire by pressing in on the tab, then twisted the grey plastic holder... I think it was clockwise (not 100% sure).. Then it should pop out. The first time it took a bit of force.
I actually put in a 5-SMD T10 bulb, but it wasn't bright enough... I thought it might be a bit dangerous so I put the stock one back in. I might order a 9 or possibly 13-SMD bulb next.