Keep all the downloaded files in one folder then right click on flashtool file and run as administrator.
It will take some time to installation the set up, then double click on flashtool folder and then open fashtool.exe in run as administrator.
Now press the BLU button at the top of flashtool and choose fastboot mode.
Then you have to select (Select kernel to Flash) and select kernel boot image from your PC.
Then switch off your phone andconnect your phone with PC until the phone show blue light on screen.
see
full post here