How?
Delete all comments
On the Reviewing toolbar, click the arrow next to Reject Change/Delete Comment , and then click Delete All Comments in Document.
Delete comments from a specific reviewer
Note This procedure deletes all comments from the reviewer you've selected, including comments that are not displayed on the screen.
Tip
You can also review and delete comments in the Reviewing Pane. To show or hide the Reviewing Pane, click Reviewing Pane on the Reviewing toolbar.