Album covers mixed up when I sync with iPhone

So I uploaded 3 different albums of music onto iTunes on my pc. Each song has a different cover and I figured out that the pc version of iTunes uses the cover of the first song as the default cover for the whole album. But when I synced my pc with my iPhone to transfer them, 2 of the 3 albums covers had the last songs of the album as the main cover, which isn't what I wanted. Does anyone know how I can fix this so that the first song in each album is the default cover when I transfer them to my iPhone?