These are the instructions to root Samsung Galaxy Mega 5.8 GT-I9150 (running on android 4.2.2) using TowelRoot App.
Requirements: Your Samsung Galaxy Mega 5.8 GT-I9150 should have at least 10-20 percent of battery to perform the rooting process.
Optional: You can also verify the root status of your device by using the Root Checker App.
[*] No data loss process: Your device Data like contacts, pictures, videos, music and etc will be not affected with the above method.
[*] Device Warranty: Once you have fully unrooted the device through SuperSU, you can claim for the device warranty.
[*] How to unroot: To unroot, Open SuperSU App > Settings > Tap on Full Unroot.
[*] Samsung Stock Firmware: If you are looking for the original firmware for your device, then head over to Download Samsung Stock Firmware page.
[*] Samsung USB Driver: If you are looking for the original USB Driver for your device, then head over to Download Samsung USB Driver page.
[*] Credits: TowelRoot App is created and distributed by GeoHot (XDA Developer). So, full credit goes to him for sharing the App for free.