Step 1: Click on the Websites tab
Step 2: Identify the property you wish to edit under the single or multiple property section and select Website Option
Step 3: Navigate to Pages
Step 4: Once in Website Pages, select the Edit button next to any active page
Step 5: By selecting Edit, you will be launched into the advanced page editor. From the advanced page editor, you will have the ability to edit image alt tags. To do so, hover over an image you would like to edit and click the green Settings button.
Step 6: Upon clicking, an image popup will appear. You will want to select the tab Image Settings.
Step 7: Add or edit your alt text and titles and select the Save Settings button.
Step 8: If you are satisfied with your changes, select Save Page button in the left hand menu.