The Golden Master version of iOS 4.1 has been released to Apple Developers, but if you’re not a developer and still want to install 4.1 on your iPhone or iPod Touch, here’s how.

Before you start, though, I have to point out that this is beta software,  so don’t upgrade if you’re worried about it breaking your phone. It’s also a developer build, so you technically shouldn’t be doing it unless you’re a developer, and while your UDID shouldn’t be checked, Apple may still get shirty that you’ve used a prerelease.

If in doubt, wait a week for the real 4.1 to release for reals.

Step 1: Download some stuff.

• Upgrade iTunes to version 10.
• Download the correct version of iOS 4.1 GM for your iPhone 4, iPhone 3GS, iPhone 3G, iPod Touch 3G or iPod Touch 2G.

Step 2: Put your iDevice into DFU mode.

You need to put your iDevice in DFU (restore) mode to make the process work smoothly. Follow the steps on the video below:

Step 3: Restore your iDevice with 4.1.

• Your iTunes should now pop up an alert to say that it’s detected a phone in recovery mode.
• Press Ok to clear the error.
• Click on your iPhone in the side bar of iTunes.
• Hold Shift (for Windows) or Opt (for Mac) and click the restore button.
• A prompt will appear asking where your firmware is.
• Select the file you downloaded earlier and press Ok.
• Your iPhone will now restore the older firmware and will reboot afterwards.

Step 4: Restore a backup.

iTunes is now smart enough to know that when you select to restore a backup of your iDevice, you don’t just want to restore the settings and leave everything else out. It’ll go through and restore all the apps, music and photos you had last time you backed up.

Step 5: Enjoy iOS 4.1 GM!

For those wondering, my iPhone 3G seems much snappier than it did on 4.0.x – almost as quick as 3.1.3, so the upgrade was worth it as I get to use all my apps again (a lot of developers don’t seem to care about anyone using an earlier version) and I don’t have a sluggish phone which is frustrating to use. Win win!