To delete your Account, first Login to your account. Click "My Account" dropdown menu, then the "Dashboard". You'll see "Profile Settings" on the left menu. You can change several sections like Account details, Personal Information, and Address details. You can delete your account from here. Click on "Delete" button from below and your account will be deleted.
If you are a contributor then read Contributor Terms to understand how deleting your account will affect your content and your earnings.