Prerequisite

Charge your phone’s battery at least 60%.
Enable USB Debugging on your phone by going to Menu > Settings > Applications > Development > Check USB debugging box
Install CWM Recovery on your Samsung Galaxy Grand first.
Do backup everything important like contacts, logs, messages with Super Backup.

Required Downloads to Root Samsung Galaxy Grand GT-I9082

Download SuperSu.zip file and paste it in SDcard of your Samsung Galaxy Grand GT-I9082.
Now power off your device and boot into recovery mode by holding Volume Up Button + Home Button + Power Button together.
In recovery select Choose Zip from SD Card and then Install Zip from SD card.
Now choose the SuperSu.zip file and then let the rooting process take place.
You have successfully rooted your Samsung Galaxy Grand GT-I9082 now.