I have a mid 2012 MacBook Air and the wireless recently started being very slow. I made sure the router's firmware was up to date and the wireless is still very slow. How can I make sure the firmware the wireless card that came with the computer is up to date? Or can I replace the card somehow? When I look at my computer's specs, it says I have a 802.11n Wi-Fi wireless networking; IEEE 802.11a/b/g compatible. What does that second part mean? Thanks!