You can click on the check box to the left of each of the Items you want to edit. Then click on the Edit button in the upper right corner. You can add, remove, or modify the category or action date for multiple items in the dialog pop-up box.
To select multiple Items at once, check the first Item in a fixed range, then hold the Shift key on your keyboard, then scroll to the last Item in the range, and click it. All items in between should be selected as well.