2 Answers

Instructions
Update iTunes

1
Open iTunes on your computer and click the "Help" menu at the top of the application window. Click "Check for Updates." ITunes checks for available updates.

2
Click the "OK" button if the "This Version of iTunes is the Current Version" dialog box appears on your screen.

3
Click "Download" in the "Update" dialog box if it appears on your screen. Follow the on-screen prompts to complete the iTunes update.

Update iPod Touch

4
Connect the iPod Touch to your PC using the iPod's docking cable.

5
Wait as iTunes detects the iPod Touch. A "download and install" dialog box will appear if an update is available for the device.

6
Follow the on-screen prompts provided by the setup wizard to apply the update to the iPod Touch. The update is complete when "OK to Disconnect" appears in the display at the top of the iTunes application window.

Read more: How to Update an iPod Touch With a PC | eHow.com http://www.ehow.com/how_8259255_update-ipod-touch-pc.html#ixzz2Cqm8Pvqj

Explanations on how to update an iPod touch, among other Apple devices, can be found at 
http://support.apple.com/kb/HT4623.