For security, you cannot delete your own member profile (even if you're an admin). Therefore, you'll need to have another member on your account delete the member profile for you.
To begin, make sure you're logged into your community website. You can do so by clicking the log in link at the top right of the website.
Next, visit your account settings.
Go to the "Members" tab, find the member you'd like to delete, and then click on the red "X" icon.
You'll be asked to confirm your decision before the action is taken. Once confirmed, their member profile will be immediately and permanently deleted. For more information on what else happens when a member is deleted, check out this article: Deleting a member.