I have just done the same due to the butane not gassing up when the temp drops into sinlgle figures. I assume that like my van the regulator is built into the van and can use either butane or propane without the need to replace regulator. If this is the case and I assume again that you will be using calor. Then the process is quite simples. Disconnect the butane bottle and remove go to the other end of the flexible tail and there is a nut which needs to be disconnected (this is just a bit tighter than hand tight). Go and buy yourself a new tail (aprox £5) this will have either a nut or thumbwheel which is left hand thread this will screw directly into the bottle. The other end will connect on to pipe by the regulator (ensure rubber seal is in the new tail) again connect by hand untill tight then just nip up. Personally then I would mix up some washing up liquid & water and paint liquid onto joints if you have a leak it will show instantly by bubbling. Oh by the way if you hand in your blue bottle they will swap at no extra cost to red. I actually went one further and they sawpped my blue for red CALORLITE which is about half the weight of normal this cost me just over £18 for the gas - make sure they sell calorlite first though.
------------- A barman is just a pharmacist
with a limited inventory