They may actually still work fine.
Unlike other dampers, Konis are set to be softer on bump and stiffer on rebound, which is why they seem to take longer to go back to full length after being compressed. If yours are still stiff on rebound they may well be OK for a while yet.
Unless they have changed (I've not used Konis for a very long time), to adjust them you push them fully closed, then the lower part engages with a slot in the upper part and you turn the two parts clockwise to stiffen and anti-clockwise to soften.
The idea is that they give a smoother ride because when you go over a bump the damper allows a more gentle depression of the springs and a slower return to normal ride height which sounds ideal. However, and the reason I stopped using them, is that if you hit a second bump straight after the first, the suspension is still partly compressed and the result can be the suspension bottoming out. For smooth(ish) roads, however, the idea is sound.