First, try learning the chords and changing between them in slow motion first. REALLY in SLOW motion, just with the left hand alone. This will help. Analyse the movements that the left hand is making. Then, make the strings dead with the left hand making the guitar like a rhythm instrument. Try playing along with a recording of the piece you are trying to play, just with the right hand strumming alone, first with downstrokes for the beat, then with downstokes and upstrokes. Imagine you are playing the drums along with the song with the deadened strings. The guitar IS actually a percussion instrument in nature. Well, then, add the chords. Try not to start with something so difficult, but with something very easy. Oldies songs are really good to start with, for they are typically easy songs with easy rhythms. Give it a try and you will see that you will make progress quite rapidly.