Samsung Galaxy Mega 5.8 (GT-I9158) Firmware Overview
The archive lists 3 official builds for the Samsung Galaxy Mega 5.8 across 1 region (CSC). The newest one is I9158ZMUANF3, released July 16, 2014 with Android Bean.
How to Flash GT-I9158 Firmware
Put the Samsung Galaxy Mega 5.8 into Download Mode, load the BL, AP, CP and CSC files into Odin on a Windows PC and press Start. Pick a build with the same or a higher Bit than the one installed — a lower bootloader binary will be rejected.