how do i resize videos from my iPhone into iMovie so that they are the correct width and height as a standard youtube is ????

Hey guys i have recorded some videos on my iphone and i have synced them to my mac.

i would now like to edit them using imovie, the only problem i have is that when i open them in imovie, quicktime, vlc etc etc, they all playback at the same width and height as the iphone screen.

now is there any way using imovie that i would be able to resize the video to make it larger so that the video is the correct height and width of a video that you would see on youtube.

If this makes sense and if there is anyway of doing please let me know as i have tried looking for a shortcut or a plug in everywhere and i just cant seem to do it.

Thanks

Sean.