Here’s how to turn off comments for all of the posts on your WordPress website:
Step 1: Log in to the backend and go to “Settings”, then “Discussion”.
Step 2: In the right-hand pane, uncheck “Allow people to post comments on new articles”. This means nobody will be able to comment on new content you upload, but that doesn’t stop them commenting on older posts. For that to be the case, another step is required.
Step 3: Check the “Automatically close comments on articles older than [14] days” option and change the number of days to “0” instead of “14”. This will effectively remove any existing comments so that they are no longer visible. Don’t forget to click on “Save Changes” at the bottom of the page to confirm your new settings.