Remove the top tube of the hi hat. You need to unscrew the hi hat rod from the linkage yoke where it comes out the bottom of the bottom tube. To do this, wrap the yoke with a rag or tape to avoid scratching it, and hold it with some pliers. Use an appropriately sized wrench to loosen the rod from the yoke using the brass coupler that connects the upper and lower rods together. This should unscrew the lower rod from the yoke. You can then remove the rod and the spring. There should be a couple of washers where the rod screws to the yoke. A toothed lock washer and a rubber or leather washer so when the hi hat is released it doesn't make a loud metal on metal sound.