Upgrading Router and or Modem

[DeadliestMoose]

I was wondering if I should upgrade to a wireless ac router, and if I do, will I need to upgrade my modem? I have an absolutely ancient SMC router/modem 802.11g and it just isn't cutting it anymore; not with my families data usage. We have 2 tablets, 3 phones, 3 laptops, and my beefy (for an ITX) desktop rig with wireless ac built into the motherboard. Any suggestions? I am seriously clueless when it comes to networking and thought I'd come here to get this question settled. We have a three story house (technically 2 since the basement might as well be a thinly veiled bomb shelter). The wife insists on keeping the thing out of sight so I either need a really sharp looking piece of hardware or something that can reach through two interior floors.