Device should be connected to PC via usb cable and installed properly with drivers that it has in it's virtual drive which appears in computer after connection. Make sure there is no sim inside device before proceeding to detect/unlock steps
Launch DC-Unlocker client
Detect device by selecting SierraWireless/NETGEAR from manufacturers drop down menu list, leave Select model as auto detect (recommended) then click magnifying glass button
Wait till program detects device
Open Server tab, enter your username and password that you received after credits purchase. Click "Check login". (you can buy credits here www.dc-unlocker.com/buy).
If DC-Unlocker/Vygis/Rocker/Infinity dongle is connected, only click " Check login "
Note: if you can't login or get error connecting to server after connecting Netgear AC778s to PC, check these settings here
Open Unlocking tab, click “Unlock” button
Wait for device to be unlocked
After you see that modem was successfully unlocked, restart it by disconnecting and connecting back. Set correct APN for different operator's card (if ou do not have APN or don't know it, it isreceived by calling operator of sim card that oyu try to use device with). Now you can use it with any SIM card