If it's a round knob with 3 screws in triangular positions, you can remove the 2 good screws and the forcefully pull the knob so the last one wrenches out. Then when you've fitted your new lock you can replace the knob but turn it a few degrees so the screws are in new timber.
It's a brute force method but quick and as any damage is hidden by the knob, it doesn't really matter.