1) Show Navigation Panels by going to VIEW menu tab.
2) Click on View Document Comments icon to bring up the Comments management panel.
3) Click on Sort by icon on the top of the Comments panel, select Type.
4) Hold down Shift and click on the first and last comment to select all, or hold down Ctrl and click on the comments you want to delete one by one.
5) Right click on anywhere on the highlight area and click Delete.