With your current hardware as described, you have two options:
- Run a cable upstairs to your un-networked router.
- Go out and buy a wireless bridge or repeater.
If your downstairs router has wi-fi capabilities, you can wirelessly network your Pis via that (assuming the signal is strong enough), but that won't get your upstairs router online without a wireless bridge.
Your typical wireless router quite simply lacks the capability of working as you're asking. It's designed to connect wireless clients to a wired network, but does not know how to route said wireless clients to a wireless network -- it doesn't even know how to connect to a wireless network itself! A bridge is the opposite of the typical wireless router (connects one or more wired clients to a wireless network), while a repeater is essentially a signal booster enabling wireless clients to connect to a wireless network they would not otherwise be able to see (due to the signal not reaching far enough).
Actually, the Pis do give you a third option (use one of them as a bridge or repeater), but that's not for the faint of heart, and even many pros would balk at that option.
Need more info... What have you tried already? Where exactly are you getting stuck while attempting to accomplish your goal? Can your router be put into WiFi repeater mode? Can it run a 3rd party firmware? Which routers are in question? etc. Please consider editing this info into your question. – Ƭᴇcʜιᴇ007 – 2014-04-16T22:56:51.910
I'm a rookie, and I don't really know what I'm looking for, so I haven't tried anything yet. I'm looking for someone to give me suggestions. I'll update with what routers I'm using. – JessMcintosh – 2014-04-16T23:03:17.327