Having played guitar for decades and Uke for years I tell folks what I do when working out a new or difficult change.
First, I am not a supporter of the "one finger at a time" method. That is just practicing a slow and inefficient way of switching chords that will limit your speed. Instead, try this...
Finger the first chord, making sure that every note rings. Carefully LOOK at and FEEL your finger positions and work on repeating the EXACT position each time. Strum the chord.
Next, PICTURE in you mind the next chord shape before you lift your fingers from the first. Then SLOWLY lift all fingers at once and move them but mentally targeting where they need to be in the next chord. Place ALL the fingers in the next chord AT THE SAME TIME. I call this "Nailing" the chord (which you should try to do with all chords anyway). Ever seen an experienced carpenter nail? They only hit it once.
When you have "Nailed" the next chord strum it making sure (like the first) that all notes ring out and there is no buzzing. Again, fix this chord by sight and feel to help your muscle memory (especially feel).
Now do this in the reverse, going back and forth SLOWLY while mentally willing each finger along the best path from its place in each chord.
It might seem crazy but if you do it this way it gets easier quicker than you might think.
After working on the two (or more) chords you are ready to work on the tune. Use a metronome if you like.
1) Play slow and steady until the change is smooth and you hit the target chord on time.
2) You need to start switching before you the chord arrives in time. Remember to "Nail" each chord.
3) When you can switch smoothly, increase the tempo and practice more.
What you are doing is separating learning to switch between two chords and then placing that switch in a larger song.
Congratulate yourself for your diligent effort and dedication and remember to take a break every 45 minutes.