You would probably want to root your LG Optimus S to install custom roms, special applications and get theme instead of whenever Sprint decides to release it. Please don’t blame me for any damage done to your LG Optimus S. LG Android Phones
Something you need to download before rooting your phone. LG-Optimus info
Now, it’s time to getting your LG Optimus S rooted, let’s go!
Step 1: Plug your phone into your PC with the USB cable.
Step 2: Make sure the phone is charge only (don’t mount as USB drive) and USB debugging is enabled. Menu > Settings > Applications > Development > check mark USB debugging
Step 3: Launch the SDK manager, should be something like C:/Android-sdk-windows SDK Manager
Step 4: Open a CMD window and type the following:
cd c:/wherever-your-sdk-tools-folder-is (mine for example is C:/android/tools)
adb push rageagainstthecage-arm5.bin /data/local/tmp/rageagainstthecage
adb shell
chmod 4755 /data/local/tmp/rageagainstthecage
cd /data/local/tmp
./rageagainstthecage (let things sit a couple minutes (2), your phone will disconnect from the computer and you’ll be removed from your ADB session)
adb shell
This should return a "#" symbol instead of a "$" symbol. If it does you’re good. If not go back and start step 5 over.
Step 5: Go to the android market on your phone and download "Superuser"(free). The developer will be listed as ChainsDD. Do the following:
-Open the Superuser application after it downloads
-click the settings tab in the top right corner of your screen
-scroll to the bottom of the settings tab and click the very last button. Should be a binary button with "tap to check for updates"
Step 6: Go back to the market and download "Titanium Backup" (free version). Do the following:
-Open the titanium Backup application after it downloads
-grant it Super User permission
-You should have a pop-up screen in front of you and one of the buttons on the bottom should say "problems". Click that.
-You can now delete titanium backup although the developer is a great guy and we recommend you consider purchasing the full app.
Please remember that rooting will void your warranty with LG Optimus S, the author hasn’t yet mentioned if it’s possible to restore the warranty by reflashing the stock LG Optimus S firmware. LG Phone Problem and Solution
LG Optimus S Phone Photos - LG Cell Phone Pictures

LG Cell Phone – Related Posts
or you can just download z4root…
z4root is quite easy to use
tried the z4root on mine and it doesnt work anymore unfortunately