Need To update My Iphone Firmware 3GS

Any Idea how to Update 3.1.3GS to 4.1
As i dont want my Iphone to get LOCKED.
any idea…. how to update. without getting the iphone Locked
MY Iphone 3GS Model - MC131B
Firmware - 05.12.01
Answer #1
Use sn0wbreeze or Pwnage Tool to create a custom firmware that will keep your baseband intact.
Answer #2
Use sn0wbreeze or Pwnage Tool to create a custom firmware that will keep your baseband intact.
How…
is it complicated, I have read some Blogs where people still get stuck
Answer #3
not so easy if u dont know what ur doing
first step is to get tinyumbrella and save all ur SHSH . official 4.2 would be out very soon …. wait for our iphone expert to give u a guidance
name is wo_0o0T
Answer #4
alright, this is quite simple.
download sn0wbreeze.
http://ih8sn0w.com/index.php/welcome.snow
download the 4.1 firmware for your 3gs  http://www.felixbruns.de/iPod/firmware/
STEP 1: Download iTunes 10.1 (or iTunes 10) from the links at the bottom of post.
STEP 2: Now start iTunes and sync your iPhone with your PC so that it backs-up all your important data including settings, apps, music, contacts and photos.
STEP 3: Download Sn0wbreeze 2.1 (links at the bottom of post) and move all these files on the desktop.
STEP 4: Launch Sn0wbreeze (please note that when used windows 7 or vista, you need to start your application in administrator mode, by clicking the right mouse button on the icon and selecting “Run as administrator”) then select Expert Mode and click on the blue arrow.
STEP 5: Now, point Sn0wbreeze to the original firmware (downloads at the bottom) by clicking on Browse and select it as below:
STEP 6: Once your device is recognized, hit the blue arrow.
STEP 7: Click on General, and check on Activate the iPhone [Hacktivate] if you are on unofficial carrier and want to hacktivate your phone by Sn0wbreeze.
Other items are optional, depends on your choices. You can’t install Ultrasn0w automatically due to some problems between the developer of Sn0wbreeze and the iPhone Dev Team.
STEP 8: At the end, hit Build IPSW to start creating your firmware.
STEP 9: Once you finished, you have to put your device in DFU mode. Sn0wbreeze will help you with that.
STEP 10: Now iTunes will detect will detect your device in recovery mode. To install the new firmware, you have to restore using the cooked firmware by clicking on the iPhone icon on the left sidebar of iTunes then hold left �alt� button (�shift� button on Windows) on the keyboard and then click on �Restore� then release the alt button, now select the custom firmware created by Sn0wbreeze and let iTunes go in a bunch of steps.
STEP 11: Well done, now you can unlock your iPhone 4, iPhone 3GS, iPhone 3G using the latest version of Ultrasn0w by following the step by step guide posted here.