If you don't want to open the computer to replace the WiFi card an easy option is getting a USB WiFi like this one, which does not need proprietary software:
https://www.thinkpenguin.com/gnu-linux/penguin-wireless-n-usb-adapter-gnu-linux-tpe-n150usb
The FSF has given it their "Respects Your Freedom" certification: http://fsf.org/ryf
