Apple is likely to launch the iOS4.0 update via iTunes for iPhone and iPod Touch users tonight. So ensure that you have the new iTunes 9.2 for Mac and Windows in order to get iSO4 update. However, Apple has not provided any set time for the uploading of iOS4 in your device. Off course you need to have a good Internet connection.
Much hyped and awaited iOS4 comes with stunning features for the devices. If you still are not aware of much of its features then you can find out about them online while Apple charged for earlier iPhone OS updates for few selected devices. Know that the first generation iPhone and iPod Touch as well as iPhone 3G and second generation iPod Touch also will not be able to get the features.
One of the things you should ensure is that your device has iTunes 9.2 installed in it and then you should connect the device to the Mac or PC with a doc connector cable when iTunes is on. Just at the time iTunes identifies your device you should click on Check for Updates button. Make sure that you do not download from links pasted on blogs or websites and different forums. Do this only when you are very much sure of the link is genuine and right for a particular device.