Samsung has just released Android 5.0 for the Galaxy S5 and there can be many reasons for why you want to downgrade to an older Android version like Android 4.4.4 Kit Kat which provides a much stabler and smoother experience.
This guide will show you how to downgrade using Odin3 v3.09.zip which you can download here. You will also have to download the firmware you want to downgrade your Galaxy S5 to, in this case we are going to downgrade to Android 4.4.4 Kit Kat G900VVRU1ANHA. You can download the G900VVRU1ANHA_G900VVZW1ANHA_VZW.zip here
If a message appears saying “Pass” you have successfully downgraded Galaxy S5 LTE SM-G900F to android 4.4.4 Kit Kat. You can now reboot your device and you will be greeted with the familiar looking Android homescreen.