Macallister Table Router

[Jerrymjj]

I've just bought a Macallister table router secondhan but cannot see how to change the router bit without removing the router from the table. Surely there is a way of doing it? I can access the router bit through the hole at the top but the manual tells me that I have to depress a lock button before being able to undo the collet nut. That is concealed behind the plastic sleeve that surrounds the mounted router. Does anyone have any advice or ideas? Many thanks.