I want to downlaod infinity blade 2. I have 1.7GB. I deleted all my apps. How can I downlaod this game?

Since IB2 is only 941mb, something else is at work. Try these two steps:

Reset the iPod:

Press and hold both the Sleep/Wake button and the Home button for at least ten seconds, until the Apple logo appears (ignore the Slide to Power Off that shows up first).

Download and expand IB2 on your computer in iTunes, then sync it with the iPod touch.

If you need to clear more space, use the colored bar chart at the bottom of the iTunes summary page to guide you in what really consumes the most room on your device.