If the lens is the older chrome lens the aperture and speed rings are locked together for EV values.
Two things I would try:
Try moving the aperture ring toward the lens mount and rotating either ring.
Second guess is a small piece of metal(?) at about the 10 o'clock position(viewed from rear of the lens)
Depress it and the pair of rings should move independently.

Be aware that BOTH the lens and body have to be cocked to remove or install a lens. If it's forced, it's not an inexpensive repair.