This is all about single finger control. You can separate the chords, first play the upper note loud, then the other notes lower.
You should also practise playing with single fingers - not using any wrist or arm action.
Put all fingers on the keys, make sure, they have contact, play with each finger, making sure the others remain on the keys and are relaxed. If you are clever, you can make up some patterns that you can play with both hands in all keys, and change the dynamics. Play it in p, mf and f.
Then you practise playing with single fingers while the others are holding the keys down (and are as relaxed as possible). You can also do this with only one, two or three fingers holding down keys, while the other fingers are playing their keys. Play it in p, mf and f as well.
Finally, make sure you know what you want to hear when playing chords with specific voicing. It helps to play the chords with two hands - one plays the accent, the other the remaining notes - especially if you want to play chords AND a melody in a single hand. What you hear with two hands becomes the model to aim for with one hand. Don't reduce that to playing the upper note louder, do that with all notes of the chords. Playing chords that way isn't usual but you will have pieces with melodies embedded in chords where this will be a good preparation.
Attention (see next post by Dan101): "No wrist or arm action" applies to these exercises only, not to normal playing!