I've used a crescent wrench to wedge under the lip and then push down on the ball to release pressure (do this outside and with the keg on it's side unless you like getting sprayed in the face with nasty old stale beer). To remove the spear there is a retaining clip you can try to pry out with a flat screwdriver and a needle nose pliers.

Micromatic is correct its fairly unusual to tear down the keg spear. My recommendation is to clean it as it was designed to be cleaned with a pump.

• keg
• pump
• coupler (with co2 check valve removed)
• basin or bucket
• somewhere to invert keg

Basically you would need a basin for what ever you want to run through the keg (rinse, caustic, sani, etc) to feed the pump. Connect the pump’s outlet to the liquid port on the coupler. Connect a hose to the co2 line to flow back into the basin (remember to remove the co2 check valve). Couple the coupler onto the keg and invert the keg (ie turn upside down). Then run the pump.

Whatever solution should pass through the spear spray the walls of the keg then drain out through the co2 pathways in the spear. This effectively is what a keg washer is doing and will pretty thoroughly clean the part you are concerned about.

A couple of safety tips: wear eye protection and make sure you purge co2 out of the keg prior to adding caustics

Good luck!