My wifi is now disabled after entering a terminal command found on this site that was suggested as a solution to a slow wifi on 12.04.
Command was
sudo modprobe -r iwlwifi && sudo modprobe iwlwifi 11n_disable=1
How can I undo this modification?
Using this command you unloaded the iwlwifi module and then reloaded it with a particular parameter. In this case the module is your wireless card's driver and guessing by the parameter's name you just disabled 802.11n support in the driver. Now try unloading it again and then reloading it without the option :
sudo modprobe -r iwlwifi && sudo modprobe iwlwifi