but this will not written any where on htc website in user manual to uninstall sync manager.
If you are outside of AT&T/Wi-Fi coverage, or the update is not found, you may perform a manual system update. This process requires that you download and install HTC Sync Manager first in order to get the proper drivers. If you do not have HTC Sync Manager installed already, you may download the software from http://www.htc.com/www/software/htc-sync-manager/
WARNING: Performing the system update manually will delete all information from the device. Ensure all information is backed up before proceeding. See the Help & How To section of this website for more information on backing up your device contents.
Performing the ROM Update:
1. Download and save the HTC One™ X for AT&T ROM update to your PC.
2. Connect your device to your PC via the supplied USB cable.
3. If the device is not recognized by the PC, ensure you have HTC Sync Manager installed and then disconnect and reconnect the device from the USB cable.
4. Once the device is properly recognized on the PC, locate the HTC One™ X for AT&T ROM Update that you downloaded. Double-click on the file to launch the system update wizard.
5. Follow all of the system update wizard instructions shown on your PC.
6. Once the update is complete, click Finish in the Wizard and the device will reboot.
7. Once the device reboots, the initial setup wizard will appear.
8. Once the initial setup process is complete, the device is ready for use.
Note: If the ROM update wizard fails to recognize the device, close the wizard and then follow the steps below:
· From a powered off state, hold VOLUME DOWN while powering on the device.
· Use the volume buttons to scroll to FASTBOOT and then press the POWER button to select it.
· Connect the device to the PC while in this state and attempt the ROM update again.
To exit FASTBOOT manually, use the volume keys to navigate to REBOOT and press the POWER button to select it.