SPD Flash Tool

 SPD Flash Tool
Step 1: Install the drivers.
Step 2: Open Flash Tool

Step 3: Pac Loading

a. Click "Load Packet". (Number "a" showed in the image). New window will appear.

b. Enter "Primo C4 after Sales" folder and select "Walton_Primo_C4_AfterSales.pac" file (number "b" showed in the image).

c. Click "Open" (number "c" showed in the image)

Step 4: Firmware Upgrade
a. Click "Start". (Number "a" showed in the image).

Step 5: Connect The Handset
After clicking the "Start", press the volume down key of your handset, and connect it to your computer with USB cable.
Remember: Before connecting the handset with your computer, you must turn it off. Also notice that the battery has to be kept inserted.
Flash operation will begin, you will see this window:

Step 6: Notification

There will appear "Passed". This means it is successful.