So what your going to do is try updating iOS on a machine that doesn't have your media (songs, videos, photos), but you have the media on another computer.
So why don't you update iOS on the computer with your media on it so it don't get deleted from the iPod?
Makes much more sense right?
Regardless you should always have a extra backup of your media, in case your computer dies or something else like a mistake happens and you can fall back on the backup.
...my iPod and computer has the same songs. I always sync my iPod with the computer that has my iTunes and everything, which is the one I'm using right now.
Good if everything that is on the iPod is on the computer, then it's no matter that your content on the iPod gets wiped during the update, you can just sync it again from the computer.
The media only on the iPod gets wiped during the update, not what's on your computer.
Well what's going to happen when you update iOS on the iPod is it's going to wipe the data off of it, so that leaves you with only one copy of your media, on the computer.
If something goes wrong with the computer, you could lose all your media.
So it's best to always have 2 copies (or more) of your media at all times so you can always restore from the backup.
To do this all you have to do is insert DVD-R's and iTunes > File > Library > Backup Library and iTunes will burn your media to the DVD-R(s) as many as you need.
Please do this often, as Apple does NOT offer re-downloads of your media and computers are flaky.