If you are not sure how to install iOS4 on your iPhone / iPod Touch you are not alone, plenty of users out there are unsure, therefore we thought we would write a quick how to guide.
To be honest Apple have made the process very simple, firstly you must ensure that you back up all important data beforehand, just in case something goes wrong. Secondly ensure that you have the latest version of iTunes installed, to do this open up iTunes, click Help and then click about, if you see iTunes 9.2 you have the latest version, if not you should install the latest version.
If you have an older version of iTunes installed click Help and then click ‘Check for Updates’, iTunes should then show a message asking you to download the latest version if iTunes, iTunes will then use Apple Software Update to download and install iTunes 9.2.
If you do not have any version of iTunes installed you should check out this link, here you can download iTunes 9.2 for PC or Mac.
Once you have iTunes 9.2 installed simply connect your iPhone to your computer, iTunes should then open (if not open it manually), under devices select your iPhone, in the iPhone summary page you should see a ‘Check for Updates’ button, click this and wait for the update to download and install, do not unplug your iPhone until the process is complete.
If you check out the source link below you can see Apple’s official iOS4 installation instructions.