Please note the firmware version in the second screen shot, earlier firmware may not work or look like this.

 

a) Plug the Ethernet cable into port1 of the inbuilt ethernet switch in the back, boot Asus.

 

 

b) Login as administrator,  browse to WAN  and Dual Wan, turn Enable dual Wan to ON, and Under primary WAN select Ethernet WAN and Lan port 1 (or which ever you plugged into)

 

 

c) hit apply

 

d) browse to WAN  and Internet connection, select WAN Type as Ethernet WAN and WAN Connection type as Automatic IP

 

 

 e) hit apply, wait while asus reboots, it might be a little slow.