I have an iPhone 4 with iOS 5.1.1, and the other day I found that it had downloaded on its own the iOS 6 update and it was sitting there in my phone, ready to be installed and taking about 2 GB of space. Since I have no interest at all in iOS 6 right now, I'd like to delete that update, but I don't know how. Does anyone know if it can be done?
I had exactly the same problem: OTA will download software updates and they take up space on the device until the user installs them. Then when the next one is released, it takes up more space. You notice them under 'Other' on the capacity graph in iTunes.
To fix I jailbroke and installed the package called "Software Update Killer". It not only prevents future automatic downloads, it deletes the software that's awaiting installation. Notice the shrink in 'Other' next time you sync. For me both 6.0.1 and 6.1 were downloaded and I recovered almost 1.5 GB.
It can probably be done if you have a copy of iOS 5.1.1 lying around on your computer, but people have had not much success doing that.
One sure way, though very tedious, is to save your SHSH blobs and use online guides to downgrade to iOS 5.1.1.