If you want to change an attribute value for numerous of products, use Bulk Product Updater:
1. Login to your admin panel and click on the Manage Products link on the left.
2. Click on the Browse categories button, highlight a category and click Go.
3. On the opened page, tick off the select box on the header of the main table. This will select all products on the page.
4. Click Edit. This will open a page where you can change attributes. Edit them and click Update to save the changes.
To add or remove attributes available on the Bulk Product Updater page go to the Admin section and click on the Bulk Product Updater link. On the opened page change the settings and click Save.