how to change encoding in mp3 tags

in itunes some mp3s don't display the correct encoding of greek mp3 tags.

The same problem exists also with some file names in windows.

An example how it looks like: Ï Óôáõñüò ôïõ Íüôïõ - Íßêïò Êáââáäßáò.

The problem exists only with old mp3s I have transfered from old PC.

Any suggestion how to fix?

Thanks

Greg