Default 4.1.2 to 4.3 Tips and Guide

Hi all, hoping to get some info regarding manual update. I am new to Android and flashing stuff on mobiles. Been checking out the various forums and havent had any luck finding a solid step guide.

So far what I have gathered information is my HTC is S-on (bootloader says Locked)

Root checker says This device does not have proper root access :/

Phone Info:
I have android 4.1.2 on my phone, software number is 1.26.502.12
Kernel Version: 3.4.10-g0a0f902
root@abm001 #1
SMP PREEMPT

Baseband version:
4A.14.3250.13_10.33.1150.01L

BUILD NUMBER:

1.26.502.12 CL166754 RELEASE-KEYS
****Locked*******
m7_ul pvt ship S-on RH
Hboot 1.44.0000
Radio 4a.14.3250.13
openDSP v26.120.274.0202
eMMc Boot
May 3 2013 19 16 59 -1


Everyone points out to this HTC news and download link but where is DOWNLOAD button it is also showing 4.4 Kitkat which I would avoid for now as my goal is to first get 4.3. Reason for that is I have read phone getting brick on 4.4 especially the AT&T ones.

Also if someone verify with the information above if this model has been modified before. ( I got a box packed AT&T sim unlocked, however the place where I am you dont get manufacturer warranty -_- as these sets come from Dubai to India and Pakistan)