Download ZTE MF825 Bolt unlocker here
NOTE: This software will work only with ZTE MF825 Bolt Firmware BD_BOLT_MF825AV1.0.1B06 Build Dec 31 2013 11:03:10
Launch software
If there is no DC-Unlocker/Rocker/Vygis or Infinity dongle connected to PC, then log in screen will appear. Use your account details to log in, otherwise you have a possibility to access software with free account that will allow you only to detect device

How to get username and password check here
Software window will appear

Connect ZTE MF825 to PC, wait minute or 2 until it is recognized on computer then click "Refresh" button, wait for device to be detected on software

Click "Unlock" button

Monitor unlock process

At the end a message will appear that unlock has beeen completed successfully

Restart device by disconnecting it from PC then connecting it back to finish the process. Now it is unlocked and usable with other operator sim cards