Please power on the S4 unit and wait for at least 3 minutes to boot up.
When the LCD screen shows you Antminer S4 with hashing status, please press and hold the button inside this little pin hole for at least 10 seconds and let it go and wait for 1 minute and power it off.
Earlier version of S4 will go back to the Static IP setup and the newer version may reset to the DHCP version.
For the Static IP version, the default network setting will be below
S4 IP: 192.168.1.99
Default Gateway: 192.168.1.99