Samsung Galaxy S4 (LTE-A/S800) (GT-I9506) Firmware Overview
What is the latest GT-I9506 firmware?
I9506XXUDRB1, released March 23, 2018 for region CRO with Android 5.0.1. The archive holds 2 official builds for this region.
Is the Samsung Galaxy S4 (LTE-A/S800) still getting updates?
Most likely not: there has been no new firmware since March 2018, so Android 5.0.1 is the last version this model got. The final builds below are still the best choice for a clean reinstall.
GT-I9506 firmware for region CRO
How to Flash GT-I9506 Firmware
Put the Samsung Galaxy S4 (LTE-A/S800) into Download Mode, load the BL, AP, CP and CSC files into Odin on a Windows PC and press Start. Use HOME_CSC to keep your data, CSC for a full wipe.