If you are new to this, TinyUmbrella or iSHSHit allows you save the SHSH blobs before upgrading the iOS which subsequently used to downgrade your iDevice firmware to an older version. Today, NotCom, Developer of TinyUmbrella has been upgraded to support iOS 5.1b1(Beta). However, currently there is no procedure available to downgrade an iPhone 4S as Apple has changed the way its signs firmware.
Before you ask; Yes a solution for the 5.x firmware nonce is being investigated… None of us have a working solution yet though. Hang tight. I have a couple trails and ideas I am trying out for 4.x baseband based restores to avoid 10xx errors. Until then save your signatures as you will never know when they may come in handy…
However, if you want to downgrade from iOS 5 Beta and have your SHSH blobs avaiable for iOS 4 then follow the step-by-step guide to downgrade your iPhone, iPad or iPod Touch using TinyUmbrella 5.00.10
You can also jailbreak iPhone, iPad or iPod touch on iOS 4.3.5 using RedSnow, iOS 4.3.3 using Redsn0w, JailbreakMe or to Jailbreak while preserving your baseband (software unlock) see TinyUmbrella, SnowBreeze & PwnageTool.