Hi
The software you can download may be limited due to the model of iPod you have e.g. I had an iPod touch 2nd generation and found (very much like you're self) that i could not update the software any more as my ipod did not have the required firmware or hardware this basically means if you want more stuff you need to upgrade!!!
If however you have a more recent generation then i can suggest a couple of things:
1: -backup you're ipod to the cloud
- plug it into you're iTunes and reset to factory settings
- and then try updating it again (while it is plugged into youre computer)
2: - again backup you're ipod to the cloud or pc then manually reset it i could tell you how to do so but I would recommend searching YouTube as a visual demonstration may help more
Hope this helped
Matt