Should be easy, I'm always having to do it for MOT's.
Just remove the seat for better access, remove the bolt at the center rear of the pipes that hold them together. Remove the two springs on the bottom inside of the down pipes ( best removed with a spring puller tool ) or like me get some strong string and feed it through on spring and round a part of the frame, pullt tight untill the hook of the srping comes out. Reverse that to get them back in. ) Remove the bolt where the pipe has a clip round it to hold it to the frame ( Carefull as there are two ali spacers each side of the bolt and they drop out )Then just cradle the right hand pipe first gently move it left and right and it will come up and out. Repeat for the left one. I'm just trying to remember if its the right first then left but your see when you do it that you have to remove one before the other can come out as its in the way.
I'm sure someone will correct me if I'm wrong.