Why can’t I change guitar chords properly?

Because you are trying to do it too fast. Try this: slow waaaay down. Put your fingers in position for the first chord and play that, Now slowly move all your fingers to the next chord finger positions- very slowly and deliberately. Don’t play the chord until you are absolutely sure about your finger positions. Are they correct? Are you sure??? Play the chord. Now back to the first chord. Once you’re sure about the finger positions (and not before) play the chord. Now back again. now do that- oh, I dunno- about a thousand times maybe. At some point you’ll have those two chords in muscle memory – you probably won’t even notice when that happens exactly. Once you have them, move on to a couple of new chords. Mainly- go glacially slow. You’ll get it, I promise. Good luck!