If you mention iOS, then the discussion resumes to Apple handheld devices and their operating system. So, to get to version 4.3 of your iOS, you should connect your device to a compatible computer which has iTunes installed because all the maintenance/upgrading and flashing operations require this software. Upgrading is easy because of the simplicity of the process involved. First, install iTunes if you do not have it and then use the USB cable, connect your handheld device to the computer and start the application. If you have a prior version of the iOS software, iTunes will notify you to perform an upgrade which in this case you should accept and follow the on-screen instructions. A backup will be created automatically in case something fails to work. During this time, your device will restart a few times and you should not disconnect it from the computer.