Now you can do it by following the instructions below.
Here’s a source from Ultrasn0w.ca that showed hot to downgrade your iOS 5.0 beta.
Many people wanted to downgrade from iOS 5 to iOS 4 Maybe you rushed out to test your app on the next big thing but now have to deal with a bug in the here and now version, and you don’t want to buy an additional device,
or maybe you just don’t have what you need yet and you’d prefer to wait for a later beta. Either way, it is possible to go back to iOS 4. Last year we showed you how to downgrade from the beta version of iOS 4 as well. I am pleasantly surprised with how good the first beta version of iOS 5 is, but if for any reason you need to go back to iOS 4, we’ll show you a couple ways after the break!
About me I don’t recommend downgrading firmware unless you really need to. It can be a painful process that most people won’t like dealing with. But if you need to, it is completely possible.
Downgrade via XCode (Mac Only + dev license)
Downgrading via XCode is probably the easiest way to roll back to a previous version of iOS. The bad part is that it can sometimes put you into a never ending DFU loop. You can typically use iRecovery to kick you out of it.
STEP 1 : Download the firmware version you’d like to downgrade to. For most people, this will probably be iOS 4.3.3 so simply find and download it via *iClarified*.
STEP 2 : After that Open XCode and from the top select Window and then Organizer.
STEP 3 : You should now see your device. Under software version, it will show you are on iOS 5. Choose to restore from Other Version.
STEP 4 : You can then navigate to the iOS bundle you’d like to restore to that you downloaded and saved in step 1.
STEP 5 : Let XCode do its thing. If you’re lucky, you’re done. If not, go to the next step. (aka if you get any error message or get thrown for a loop via DFU craziness.)
STEP 6 : You’ll need to use a program like iRecovery which is linked above. I use Faster iRecovery as opposed to the original. Also, download the libusb files for Mac as well. iRecovery uses these.
STEP 7 : Simply run iRecovery after you’d downloaded the libusb files and it should throw your phone out of recovery mode.
STEP 8 : After this, simply restore in iTunes and you should be downgraded. The first time you may get an error, simply restore again like you normally would and it should downgrade successfully.
As a side note, PC users can also use iRecovery and libusb if they get stuck in a DFU loop.
Downgrade via iTunes beta with TinyUmbrella (Mac and PC)
You need iTunes 10.5 beta for this, which is also available via Apple’s dev portal (and maybe elsewhere if you scan the internet)
You also need TinyUmbrella:
This is the route PC users will have to take. Mac users may also choose to do it this way if they don’t have XCode or the SDK. Start this process with your device NOT connected to your computer.
STEP 9 : Install iTunes 10.5 beta and TinyUmbrella
STEP 10 : Then open TinyUmbrella and click on Advanced.
STEP 11 : Uncheck the box that says Set Host to Cydia On Exit.
STEP 12 : Restart your computer.
STEP 13 : Now plug in your device and turn back on your computer.
STEP 14 : After your computer restarts, you’ll need to go into iTunes. It may bring up error messages again. That’s okay. Just ignore them for now.
STEP 15 : You’ll need to put your device into DFU mode. Refer to our DFU mode instructions if you’re not sure how to do this.
STEP 16 : If you don’t do it correctly, just try again. When you get your device into DFU mode correctly, iTunes will pop up and tell you the device can’t be used until it is restored.
STEP 17 : You can now restore your device like normal.
Personally I have done this before, but you guys can try and report it here.
Thanks!