
Samsung Galaxy W
The latest firmware for Samsung Galaxy W (SM-T255S) is T255SKSUAOI2 with Android 4.3 (Jelly), released on September 10, 2015 for 1 region (CSC). Every official firmware build for SM-T255S, 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/T255SKSUAOI2
All 3 builds in our database run Android 4.3 (Jelly). The newest build, T255SKSUAOI2, was released on September 10, 2015. No new build has appeared for 135 months, so regular updates for this model have most likely ended.

SM-T2558

SM-T2519

SM-T350X

SM-T357W

SM-T355C
The newest firmware for SM-T255S runs Android 4.3 (Jelly): build T255SKSUAOI2, released on September 10, 2015.
The latest build for SM-T255S, T255SKSUAOI2, was released on September 10, 2015 (11 years ago).
SM-T255S has had no new firmware for 135 months, so regular updates have most likely ended.
Yes, all firmware files for SM-T255S are 100% official, original, and obtained directly from Samsung servers.
To flash SM-T255S, 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-T255S.