If your lamp shade has seen better days and the ring is looking a bit worse for wear, then it's time for a change. Here's how to do it:
First, remove the old ring from the shade. To do this, simply unscrew the retaining screws (usually located at the top and bottom of the shade) and carefully pull off the ring.
Next, measure the inside diameter of the new ring against the outside diameter of the shade. The fit should be snug but not too tight - you don't want to damage either piece.
Once you're happy with the fit, screw on the new ring using the retaining screws, being careful not to overtighten them.
And that's it! Your lamp shade should now be good as new.