Fuel Filler Lock Barrel removal

Hello All,
Help please.
I am having problems with the fuel filler cap on my Freelander 1. It has become difficult to remove & refit. I have obtained a new filler cap but need to know how to remove the lock barrel from the existing cap & fit it to the new one.
Any help would be most welcome.
Thank you
Regards
Bfc99

are you sure its the filler cap mechanism that's at fault and not the lock itself