the restriction code is a code used either from companies to restrict the access to certain networks ..or set by the owner for to restrict the contain or browsing ..
If you know the password its easy ..just get to settings ..and remove the restrictions ..if you are talking about other codes..try to jail break it like the ones in these videos ..(It a software you should use ) http://www.youtube.com/results?search_query=how+to+unlock+ipod+touch+restrictions&aq=0m
I understood that there is another way to get the code..by using a file manager and browsing the internal files and retrieve the ones containing the password..but for apple products this is difficult cause of lack of browsing managers..
So try jailbreak ..or reinstall the operation system..if you really want to remove the codes and it is not just an informative question ..
no matter what codes are active ..if you reinstall (update firmware ) ..this will get it from scratch ..and all settings will be gone ..But remember it is a delicate operation ...see the support site and read about it ..