Welcome to Vodafone Community
The best place for advise would be to contact the Broadband Team here: Broadband and Home Phone FAQ's
The problem you may have is Superfast uses BT Openreach infrastructure where Gigafast uses City Fibre, meaning a separate installation. There is further information for Gigafast here: How is Vodafone Gigafast broadband installed?
- as long as Gigafast is now available in your area, you'll be able to upgrade from Superfast without any termination fee; or early upgrade fee. This will of course start a brand new 18 or 24 month contract.
I was going to go with Virgin, but now I will sign up with Vodafone, Cityfiber are still installing there network in my area right now. No idea when will go live hopefuly latter on in the year. Great news if get Vodafone Superfast (Openreach) now and at latter date hopefully soon I will be able to just change over Vodafone Gigafast (Cityfiber) with no early termantion chages.