Many of you know that Samsung recently released a variant of Galaxy S4 that runs vanilla Android. You can have it on your GS4 too if you want. All you have to do is download a ROM and flash it in recovery.
So, get the firmware from here and copy it to your external/internal SD card. Then, boot to recovery by pressing vol up and power button at the same time. Wipe the data and dalvik cache.
Select the option, "install zip from SD card" and browse for the file you copied earlier. Let it flash itself. Reboot the phone after flashing is done.