
Samsung Galaxy Amp Prime
The latest firmware for Samsung Galaxy Amp Prime (SM-J320AZ) is J320AZTUS3BQL1 with Android 7.1.1, released on December 10, 2017 for 1 region (CSC). Every official firmware build for SM-J320AZ, newest first: one row per build with all regions (CSC) that received it.
Each firmware build has its own page at https://samfirm.shop/build/{PDA}, where {PDA} is the build number from the list above. Example: https://samfirm.shop/build/J320AZTUS3BQL1
Specifications of SM-J320F, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-J320VPP

SM-J327VPP

SM-J326AZ

SM-J337A

SM-J330N
You can find the firmware on the model: SM-J320AZ page.
Yes, all firmware files for SM-J320AZ are 100% official, original, and obtained directly from Samsung servers.
To flash SM-J320AZ, you need to download the appropriate firmware, put your device into Download Mode, and use the Odin tool to load the BL, AP, CP, and CSC files.
Downgrading is only possible if the bootloader version (binary bit) of the old firmware matches the current one. Always check the binary version before flashing SM-J320AZ.