What kinda mags are they? Pistol, rifle, caliber, etc...
One old trick; take the ammo out, then place the mags in a WARM oven for 2 hours, then take them out and let sit for 48 hours.Lubricate with white lithium grease.
With the proper equipment, some mag springs can be changed.
But, you should never let rounds sit in a magazine for a long period of time.
I've seen other mags that seem to have the bottom plate held in by drift pins. You'd need the appropriate tools to get them open.
Still other mags seem to be glued, soldered molded or crimped together. The problem might be where to get the correct replacement spring. I haven't seen any, but then I haven't looked.
Check with a gunshop to see if they can get them repaired for you.