Step 1: Download the flashable .zip file from here.
Step 2: Once downloaded, place it under the /sdcard directory of your Desire S or Desire HD and power your device down.
Step 3: Initiate ClockWorkMod Recovery by holding Volume Up + Power.
Step 4: Take a nandroid backup.
Step 5: From main menu, perform a factory reset (wipe cache partition and from the advanced menu, opt for wipe Dalvik cache.
Step 6: Go back to the main menu. Do install zip from sdcard > choose zip from sdcard and select the downloaded .zip file you placed on your SD Card in Step 1.
Step 7: Once the firmware has been flashed, do a reboot system now.
