Depromoted or Demoted

Is it okay to say, ‘He’s been depromoted’?

No, it isn’t. Although ‘depromoted’ is a possible word, it does not exist; no dictionary lists it. The word that you have in mind is ‘demoted’. When you ‘demote’ someone, you lower his rank or position.

After the trial, my cousin was demoted from colonel to captain.

Courtesy : Know Your English -The HIndu