We currently have a modem/router that is on the lower level of our house. We have 2 offices on the second story, and I'm trying to figure out the easiest way to get direct connection up there. Currently my plan is to run ethernet cables from the modem up to the office and have it connected to a wall port. I don't know a ton about networking so I didn't want to mess with switches or anything. I just wanted to make sure it wouldn't hurt to just run cables from the modem to the wall ports.
If you can run a cable up to either office and attach it to a wall RJ45 socket, you can then attach either a small (5-8 port) unmanaged switch or to an inexpensive router configured as an access point, which would give you the three unused LAN ports as a switch and wireless upstairs. Unmanaged switches take no effort, they are plug and play -- sort of a "cable splitter" and everything will still be routed by your downstairs router.