Can anyone give me a lesson on how to change from one chord to another or what chords go great together?
To practice changing chords, take 2 chords that you can play fairly well and just slowly go back and forth between them. Focus on keeping your muscles fairly relaxed and which finger moves where. Once you can get the change well at a slow pace, gradually play it faster until you can do the change at the required tempo every time. Do this every time you have trouble changing between two chords.

As for what chords go great together, the simple answer is chords in the same key. To get a better understanding of this you need to learn some basic diatonic theory.
Learning to change from one chord to another can only be learned through repetition. And I mean a lot of it. Just pick 2 chords and go back and forth between them as slowly as it takes to get it right. Then increase your speed, staying only as fast as you can do it cleanly.

As far as what chords sound good together, all the chords in the key you are playing in all do. There are other appraches to "what sounds good" because it's a matter of taste. Some of the most popular music consists of dissonant chord changes because they are interetsing to your ears and make them want to listen for what's coming next.

But, as far as which chords always work together from a theory perspective, try learning the diatonic sequence of chords for each of the 12 Major keys. "Dia" meaning to move through, and "tonic" meaning the tones or notes of the scale or key.

Check out www.reallylearnguitar.com/majscalestutorial.htm, www.reallylearnguitar.com/chordformulas.htm, and www.reallylearnguitar.com/triadstutorial.htm and you'll be well on your way to understanding what always naturally fits.
Jam On!