at first, I have to admit, that I started flashing oder playing with my ZTE Open C started last week.
By now I flashed different images and had some issues also.
I started with the Open C Upgrade Tool from comebuy Firefox OS developer site. At mozilla ZTE Open C site you will find this link. But that image has issues with recovery.img and so i installed on my Ubuntu these packages android-tools-adb android-tools-fastboot.
Now you have to start your mobile into fastboot-mode by switching off your mobile. Then press start button on top off your mobile and volume control down button the same time. Then you will see splash image and your mobile will be in fastboot mode. Open terminal and type "sudo adb start-server" connect your mobile to laptop and type "sudo fastboot devices" now you will get a message. Download the images from vampirefo from the other thread or just download cw_recovery_50.img if you have done this you can boot this img on your mobile: "sudo fastboot boot cw_recovery_50.img". Then just wait. You will see after some time a menu where you can select backup or recovery. Then there will be a second menu and you can select a backup to external_sd.
I hope i could help you with this.
By the way... If you don't run Ubuntu, you need some android-sdks for Windows.