hi, the conversion kit you require is called a regulator the butane cylinder will have one of these, http://www.ebay.co.uk/itm/CARAVAN-CAMPER-BUTANE-REGULATOR-CALOR-CLIP-ON-TYPE-/200754378874?pt=UK_Campervan_Caravan_Accessories&hash=item2ebde4b87a
the propane cylinder requires one of these,
http://www.ebay.co.uk/itm/NEW-LPG-red-PROPANE-gas-regulator-caravan-camper-bbq-/120581626729?pt=UK_Campervan_Caravan_Accessories&hash=item1c13399b69
you have to cut off he old one and replace it with one of the other types make sure you use a new pipe clip , I would suggest that as it is gas you are interfering with uless you are 100% sure of what you are doing you get someone to do it for you,
as an aside once you have changed over the bottles there is no need to change back to butane as calor will exchange the blue bottles to red at no extra charge and propane is better for winter use as it does not freeze in cold weather. I converted to propane last year as the new calor lite bottles only come in propane,
colin