Everything JeffS65 said, although I particularly lke this:
"Patience is the best friend of a guitar player. Well, after a while you want every guitar on the planet so, so the true best friend is money (hehe) but a close second is patience. Just go back and forth and get used to the movement."
The keys to training your mind & body to change chords initially are in this sequence,
1. form the chord shapes properly,
2. don't be concerned about speed [u]initially[/u]. That's a WIP,
3. repetition, ...repetition, ...repetition until rote.
i.e. to learn those two chord shapes and achieve smooth sufficiently fast changes to render them practical, start by forming each chord individually over and over and imprinting the shapes. Keep at it, each for as many minutes as you can before your mind wants to go numb, have a [u]short[/u] break, then do it again. Make sure you strum after forming to ensure the individual strings are ringing clear indicating you are fretting properly. It also gives your other hand a coordination workout hitting A. the target strings only & B. working in concert with the other. Once you have that down, work on changing back and forth between the two chords, which will later become three and more chord exercise. e.g. A to D, back to A, to E, back to A, to D back to A continued ad infinitum being one such fairly easy example. Speed is not important initially. Like riding a motorcycle fast through the twisties, focus on achieving [u]smooth[/u] and speed will naturally follow effortlessly with repetition and time.
Just achieving the change smoothly from one chord to the other forming them properly and as slowly as you must to do it is the [u]initial focus[/u]. Once you can do that with sufficient competence, take a metronome and note the rate you can currently change those chords at. If that's not the practice song speed, note what it is. Now increase it incrementally by 5 or 10 BPM. You speed [u]will[/u] increase with repetition. Keep doing that until you have the metronome at the tempo required of the song you want to play or the practice piece Lisa has presented and can change with it. Now play the piece you want to. When you find you can do it, the positive reinforcement of success will both remotivate you and provide you with confidence as you approach the next challenge.
That said, don't be too concerned with two string "simple" fingerings. e.g. Am. As previously stated in an earlier post, their raison d'etre is as easy starter confidence builders. You'll be taught and using the correct open fingerings very shortly.
Re [u]piano's relevance to guitar[/u]. Although my focus remains very much with and on guitar, I recently bought myself a Yamaha keyboard motivated by (i) curiosity, and (ii) to expand and compliment my understanding of both the theoretical and pragmatic aspects of music. A keyboard neophyte, I was astonished to discover how linear the keyboard is compared to the guitar neck, exactly as JeffS has described. But that said, whilst they share in common that they are both musical instruments using the same seven notes, possibly the best analogy I can think of is just because you have learnt to drive a car doesn't mean there's a [u]significant[/u] crossover in the [u]demonstrated[/u] [u]doing[/u] part in attempting to learn to pilot a plane just because they share in common both being (electro-) mechanical machines.
