How do I upgrade to a full membership?

Ummmm... you don't. You already have one. We don't have different levels of membership like other sites claiming free access but that limit what you can do until you pay. We are a totally free site, with no limits (except for the amount of space we give you for photos, 'cause we're not flikr and don't want to be... they already do it way better than we could). So send all the private messages you want, look at all the profiles and photos you want, participate as much as you want in the forums, etc., etc. You already have a full membership.