Hi Abhilash,
I have tried this kb [KB 17410] works. The only thing here is that it takes a hell lot of time. reason being serial mode of transfer.
Have patience... it will copy the junos image. Don't forget that the image itself would be a huge file.
Besides if you have physical access to the device you can try the usb method to copy junos as :-
log into primary node after inserting the usb to secondary & then try :-
>request routing-engine login node 1
%mount -t msdosfs /dev/da0s0 /mnt [ check the correct drive by running ls -l /dev ].
%cp /mnt/<junos package name> /cf/var/tmp/
%
Now you are ready to upgrade the devices.