Using your DeWalt DZO400 7.5-inch Replacement Edger Blade is easy. First, make sure your edger is turned off and unplugged if it's an electric model. Then, carefully remove the old blade and install the new one following the edger's user manual. When using the edger, keep a steady pace and apply gentle pressure for clean and even cuts. As for safety, always wear protective gear like goggles and gloves. Avoid using the blade on hard objects like rocks, as this can damage the blade. To maintain your blade, clean it after each use with a brush to remove dirt and debris. Store it in a dry place to prevent rust. If you notice any signs of excessive wear or damage, replace the blade promptly to ensure the best performance of your edger.