Self- dan External-

External improvement is the kind of improvement that could be gained (or lost) by the body-swapping scenario. Money, fitness, credentials, status, friends, etc. are all external improvements.

Self-improvement is the kind of improvement that wouldn't change in that scenario. Habits, thought patterns, confidence, beliefs, learned skills and behaviors are all internal improvements.

Obviously the two kinds of improvements influence each other. Being rich may start to improve your confidence. Similarly, being disciplined and frugal may start to make you rich. The two interact in all sorts of complicated ways.