Wikipedia:Courtesy vanishing

The usual way to leave Wikipedia is simply to stop editing and abandon your account. A courtesy vanishing may be implemented when a user in good standing decides not to return and for whatever reason wishes to make their contributions harder to find or to remove their association with their edits. When there is no administrative need to retain the information, a permanently departing user may request that a wide range of user pages, and other pages that affect them alone, be deleted on departure. The user account is renamed; user pages are blanked or deleted; and pages related to the user's conduct may be deleted, blanked, or moved. Contributions, logs, signatures, and user-page templates (for example, templates related to blocks or bans) are usually not removed. User talk pages are usually not deleted.

Courtesy vanishing is discretionary and may be refused. It is not intended to be temporary. It is not a way to avoid scrutiny or sanctions. It is not a fresh start and does not guarantee anonymity. Any of the deleted pages may be undeleted after a community discussion. If the user returns, the "vanishing" will likely be fully reversed, the old and new accounts will be linked, and any outstanding sanctions or restrictions will be resumed.

As all contributions are licensed under the CC BY-SA 4.0 License and the GFDL and therefore must be attributed to a user, it is not possible to delete an account.