How to jailbreak ipod touch

First of all, I am not sure if that is the right term or not. I just bought an ipod touch and want to be able to upload music from another ipod and itunes from another computer. Both Ipod and other itunes are mine but cannot seem to copy from one to the other easily. I use both ipod and don’t want to unlicense (or whatever the term) is either one. Is there a way to do this safely? Thanks for the help.