I'm not completely sure you are able to, but here are the pages to look for

So you want to edit the Fibre WAN connection, it doesn't have a specific option to disable VLAN like MyRepublic requires so you could try 0.

Make sure you're in advanced mode to find these settings. The VLAN should be the only one you have to change as Vodafone and MyRepublic both use IPoE / DHCP

MyRepublic - Setting up Third Party VDSL & Fibre Routers

I haven't spent ages on it, and don't have one here to play with, but I've not been able to get the ultra hub to successfully disable VLAN on the WAN port when I have tried. Even though it might say it is, it didn't seem to work.

They are pretty locked down.