To change your Virgin superhub into modem mode, you need to log into the router (I'm going to guess that you haven't changed the password from the one on the box). I think it is on the home screen where you can switch to modem mode.
Most routers will work fine out of the box for you without...
As said previously, don't mix up broadband with wifi. I know people will think it should be part of the package (rightly so) but if you want to get better, more reliable wifi in the house then stump up the cash and buy a good router.
Having got some recommendations from the Virgin forum, I...
The Virgin superhubs are well known for having wifi issues if you look on their support forums. My wifi kept dropping out or hanging and it was becoming a real pain. I decided to invest in a TP Link router and switch the superhub into modem mode and haven't had any problems since.