iOS 4.2.1 is the latest version that the 2nd gen Touch can run. When you check for updates, you will see a message telling you that your iPod is up to date.
The successor to the 1st-generation iPod Touch, it was unveiled and released at Apple's media event on September 9, 2008. It supports up to iOS 4.2.1, which was ...
I also have an iPod touch 4. It runs iOS 6.1.6. Also, I would like to install Club Penguin: Puffle Launch and Bad Piggies. I will go find some IPAs of them.