How do I convert a movie off of itunes into a different format?

I have a ipod nano generation 5. I downloaded a movie off of itunes and its in the MPEG-4 fomat. My ipod only takes: AAC (M4A, M4B, M4P, up to 320 Kbps), Apple Lossless (a high-quality compressed format), MP3 (up to 320 Kbps), MP3 Variable Bit Rate (VBR), WAV, AA (audible.com spoken word, formats 2, 3, and 4), AIFF. How can I convert it to one of these formats? I'm really upset!! Please help me!