You can delete a candidate from the database by this way:
- selecting him from a search list and then clicking on the Delete candidate(s) function, in the drop-down menu Select
- clicking on Candidates > User Account Admin > Icon 
beside the candidate > Delete Account > Delete
- Automatizing the data retention process as indicated in the following article: https://inrecruiting.freshdesk.com/a/solutions/articles/14000015922
NB: due to the cancellation of a candidate you will lose all plotted information about the candidate himself, who will also receive a notification of cancellation automatically sent by the software (to edit the e-mail: System settings > E-mails > Candidates > Account deleted: Confirmation).
In the Privacy section of the General Settings, it's possible to decide whether to send the cancellation notification to the candidates: to activate this function, simply click on YES and the other way around to deactivate, simply click on NO.
The candidate may also request the deletion of his profile, which is not automatic, but must be confirmed by the Company User (you'll find the request in Candidates > User Account Admin. Also, if you have set an e-mail in System settings > General settings > Privacy settings > Notification recipients for privacy settings you'll receive an e-mail alert every time a candidate asks to be deleted).