Four tips not included in that article:
there may be a small set screw with an allen head that goes into the bottom of the lowest tube concealed under the grip frame. It means the gun has had a valve job. It MUST be removed before tapping the valve out of the body or it will destroy the gun's internals. Use something to air seal it when replacing it after the valve is re installed.
If you don't h ave the special steel punch shown in that article, you can drop a used 12 gm in the front of the co2 tube and tap the back of it to drive the valve assembly out. DON'T use any other punch or it may destroy the valve seat. Don't try to drive it all the way through, it won't go.
Throw the lead seal away and don't replace it.
The article shows reassembly with the gun sideways. I find the best way is to hold the tool straight up with the valve components balanced on the top. Hold the gun straight up in the air and slide the assembly in.