Removing a FD/FL lens from the adapter.
Depending on the Canon FD lens you have there is one of two ways to remove it. If your lens is the older breech style lens there should be a thick silver or black colored ring against the adapter, this whole ring rotates to unlock the lens from the adapter (the lens itself stays stationary while the ring is the only part that rotates to unlock the lens, see attached). If the lens is the newer bayonet style then there should be a tab or button to press to unlock the lens so the whole lens can rotate off the adapter (see attached).
The ‘lock/open’ ring on the adapter only controls the aperture of the lens (locks it down to the smallest opening set for metering and shooting or opens it up to the largest opening for viewing). It does not have anything to do with removing the lens from the adapter.