Best and most safe route is to let your phone tell you when a firmware update is available and or manually check in your phone's software update section.
If your looking for firmware due to some sort of corruption or failure then Vodafone apply a 24 month manufacturing warranty on a phone as long as accidental damage isnt present.
Vodafone UK wouldnt send you the files for their firmware.
Other route us to Google for custom Roms but be aware that route can bring further issues if not carried out correctly.
Current Phone >
Samsung Galaxy s²³ Ultra 512gb Phantom Black.
