Having repaired a
LOT of equipment over the decades, it's often quite difficult to remove wires, and if you're not careful you can break the connectors, or the wires. As JimB suggested, it's often a matter of pushing or pulling something to unlock it - sometimes you need to push both sides while you pull the wire with your third and fourth hands
Othertimes the socket will 'latch' in the unlocked position once you finally figure out how to activate it, and gentally moving each side in turn might be one technique.