Why my samsung galaxy s5 g900a of3 could not update to android 6.1?

[Android Central Question]

HI
I WAS LOOKING TO UPDATE MY PHONE (S5 G900A) TO ANDROID 8.1 BY CUSTOM ROM...SO THAT I HAD TO DOWNGRADE THE ANDROID TO 5 TO CAN BE ROOTED.IN CASE I DIDN'T ATTENTION TO THE BUILD NUMBER (OF3) AND DID NOT FIND ANY CUSTOM ROM FOR MY PHONE!
Now i am looking for to update my android to 6 version but i cant do it due to it has now a custom Rom of android 5...
when i am trying to update it from setting it says you are using latest update!!!
what can i do now?
please answer my question
thanks.

 

[Rukbat]

The latest update was to 6.0.1 (the April 2017 update - QD1). The March file (QC1), the latest one I could find, is at https://androidfilehost.com/?fid=745425885120723808. (Whether that's the update or the full firmware I'm not sure, but at 2GB it's probably the full firmware. Just load it into Odin (the AP slot if it's a single file) and flash it. If AT&T still has the April update out, you should get it in a week or so at most. (Or once you've flashed it, you could go to Settings and try to force an update to QD1 (in About Phone, if I remember Marshmallow.)