Noob question on winrar maps

Hi sry if this has been answered but did a search and could not find much on it, I think i'm just being a noob anyway but downloaded the GBireland winrar files from the ftp site, parts 1-4. When i extract the first part i get GBIreland.iso, but they all extract with the same name. Do i need to combine these 4 iso's some how?
Should i be extracting them with different names GBIreland1.iso etc then combine them to form one iso to burn to disk?
Any help would be appreciated thanks.