You will want to search, there's been many different threads on it but here's the jist:
Get a drill bit extention rod at least half the langth of your muffler.
Depending on your muffler outlet hole you want a drill bit as large as you can get into the whole of your muffler. I think mine was a 1" hollow hole bit (kinda like the kind you would make a door knob hole with but smaller.
I had to use "an assistant" to hold the muffler in place. You could use a vise but don't jack up your muffler.
Get your drill and go to work. You will hit a couple different "walls" in the muffler and drill through them. I went all the way down until I could see light at the end of the tunnel. Make sure you get out any bits that fall into the muffler.
Note that some people required "jetting" because the mixture became more lean as a result of riding with no exaust pressure. I did not notice a significate loss of performance at all, however my header pipe bluing got worse.
There's a sticky with Jetting set up. If your not willing to risk your only set of Mufflers you should buy mine and keep yours as a back up
That's why I have had mine for so long, but now I know I'm not going back.
Good luck.