Go to Settings in the top navigation bar. 
Click on Account, then Networks.
Go down to the Join a Network section. Enter the network access code you received from the network's owner in the Access Code field and click Join Network.
Go to Settings in the top navigation bar.
Click on Account, then Networks.
Go down to the Join a Network section. Enter the network access code you received from the network's owner in the Access Code field and click Join Network.