1- Download LYF LF 2403 Flash file which consist of File, tool & Driver.
2- Install Driver
3- Connect Phone in ON mode to cross check driver installation. It will make port named "Qualcomm HS-USB Diagnostics 9091"
4- It means driver has been installed successfully.
5- Install Flash Tool, which will install shortcut on Desktop named QFLASH Tool.
6- Connect phone & Click on Load Content and from Flash File Folder select Content.xml
7- It will show Port in tool.
8- Click on Download Content to start Upgrading.
9- Wait till done appears.
10- After upgradation, device will shift to download mode.
11- Disconnect Phone & reinsert battery.