Unfortunately, you can not delete your cTrader ID.
Your broker or Spotware(the developer of cTrader trading platform) cannot delete a cTrader ID either.
Instead, you can unlink your trading account from a cTrader ID, in order to link the account to another cTrader ID.
To unlink your cTrader trading account from a “cTrader ID”, you need to request for it to your broker directly.
Alternatively, you can also change registered email address, username and password of your cTrader ID anytime.