I suggest you watch this video before you do anything else. It covers the basics of adjusting wooden planes and may well solve your problem.
Apply the techniques. Rap the heel of the plane with a wooden mallet to loosen it. If that doesn’t work, you may try tapping the iron down as that will typically loosen the blade/wedge. If all else fails, drop it off your bench so it hits butt first! That usually makes everything fall out on the floor! (just kidding…sort of).
It is also possible that the plane body has changed size due to wood movement and it may be literally crushing the wedge between the sides. So if you can’t get the wedge to come loose using any of the techniques in the video, consider drying it out – put it in a 150 degree oven for a couple hours.
Bear in mind – if your plane has any historical significance, or personal sentimental value, you may want to take it to a qualified restoration expert. Any of these techniques, if applies improperly or even if you just have a bit of bad luck, can permanently damage your plane.
Best of luck.