Now go to HTCDev.com and Register for an account.
Once registered, go to the home page of HTCDev.com and select Unlock Bootloader.
On the right of this page, select the HTC Wildfire S on the dropdown box and Click Unlock Bootloader.
Accept all the long disclaimer messages, and click proceed to install instructions.
Now, scroll down to the bottom of the page. Find the ROM which has the same number as the kernel version you noted down before and download it. If you cannot find your ROM scroll to the bottom of this post. For example, mine was 2.13.401.3 so I downloaded the HTC EU one.
Once it has downloaded, plug in your phone, make sure USB debugging is enabled and open the file you just downloaded from HTCDev.
Now, follow the on screen instructions. It should be fairly easy.
Once it's done Congratulations! You have updated your bootloader.