Steps to  delete someone’s Reddit account:

• You can choose to 'deactivate' your account on Reddit. This deactivation is irreversible. Your profile will be permanently removed from Reddit after you deactivate (delete) your account, and your username will be removed as well.
•  Any Reddit posts or comments you've made, on the other hand, will stay on the site. They just won't be associated with your Reddit username. They become 'unattributed,' as Reddit calls them, and no one knows who uploaded them. Messages you've sent will be de-identified as well.
• Go to your Reddit account settings page to remove your account.
• You can discover it by selecting 'User Settings' from your name in the top-right corner of the Reddit website.
• Click the red 'Deactivate Account' link at the bottom of the page.
• Reddit will ask you for feedback on why you're deleting your account. To proceed, enter your username and password, then select ' You  realise that deactivated accounts are not recoverable' and 'Deactivate.'
• Reddit will ask you one last time for confirmation. If you're sure you want to go ahead with it, click 'Deactivate.'

Read More: How does Reddit work? How can I use it effectively?