If your iPhone will not update to version 5 and you have Kaspersky Internet Security installed there may be some network blocking that interrupts the installation. Here’s how to disable it:
Open Kaspersky main window and select Settings > Application control > Applications. Expand the Apple branch by clicking on the plus next to it, then double click Itunes. Go to the Exclusions tab at the top and tick all boxes. Click on OK then click Apply and it should update without problems.
Another option is to temporarily disable Kaspersky by right clicking the tray icon and selecting Disable protection. Importantly, check you are behind a hardware firewall first such as a router before disabling any firewall. You will find that similar firewall and internet security products can cause instability and errors when updating Apple’s iTunes.