Exhaust pipe extension

Go to NAPA or Autozone. Most any Auto supply will have a Chrome tail p[ipe part for you. I have put them on several Coupes...

I'm looking for an exhaust pipe extension for my 415D.  It needs to have an OD of 2 1/2" and be at least     6" long.  Vernon had one but it was too short.  Pictures attached.  I'm actually not sure how to get the old one off. Cut it?  How to install the new one.  Clamps? Screws? Thanks.