I am assuming that you mean a photo which was taken in portrait mode when imported into Movie Edit Pro (MEP) is on its side in landscape mode and when you rotate it to the correct orientation black bars appear on both sides and the image is full height of the preview monitor.
Adjustments available to you are:
Increase the width of the imagekeeping the same height - this makes the subject short and wide - ie is going to be distorted in the horizontal direction - not very flattering for shots containing people
Crop the image to fit the width of the screen - you are going to lose a portion of the image top, bottom or both.
See this topic on a related issue if you have MEP Premium.