You can change your account by going into MobileMe preferences, I think you can purchase additional storage there, but I'm not sure about upgrading from an individual to family. That might have to wait until your current deal expires.
As documented on Apple's mobileme page, yes you can change an individual to a family, just not yet. Mobileme of course is still going through some teething problems and the billing section isn't showing up yet to make the upgrade. Give it time
I bought the Family plan while I was in the store. I already have a .Mac single user account but they were offering a discount in the Mobile Me family plan so I bought that.
As documented on Apple's mobileme page, yes you can change an individual to a family, just not yet. Mobileme of course is still going through some teething problems and the billing section isn't showing up yet to make the upgrade. Give it time
Yes, I think we have to wait awhile. I tried upgrading to family when it first went up. The button to upgrade is no longer there. Apple removed it temporarily.