To be able to update the software on your device, you must first download the appropriate IPSW update / restore file. While iPhone owners always get these updates for free, iPod touch users must pay for the major software releases, as was the case with iPhone OS 2.0 and 3.0. If you own an iPod touch and 3.0 is how you roll, the 3.1.3 release is also free for you.
With that out of the way, Apple wants everyone to update the software on their device by connecting it to a computer running Mac or Windows with iTunes installed. iTunes will do its job of notifying you that iPhone OS 3.1.3 is available, and will offer to download it from the company’s servers, and install it for you automatically. iTunes also provides you with the option to select the firmware bundle (IPSW) to which to restore your device.
With the felixbruns.de all-IPSW download source, and the jailbreak tools from the iPhone Dev Team, device owners can also free themselves from the restrictions imposed by Apple, by jailbreaking the firmware, although this isn’t necessarily a wise decision. It is also worth noting that, using the aforementioned IPSW download source, iPod touch owners can also trick the system and get their updates completely free of charge. We advise against it, of course, and take no responsibility if Apple catches you and slaps you on the wrist.
Downloads are currently available for the following IPSW files and their respective devices:
iPod touch- iPod1,1_3.1.3_7E18_Restore.ipsw;
Finally, Softpedia itself is at your service if you own an Apple iPhone and want to update to firmware 3.1.3. Simply use the download link at the bottom of this article and select the appropriate firmware bundle for your respective device. You can then use iTunes to selectively restore to it whenever you want.
Download iPhone OS / Firmware Update (Free)