1. Yes, you can re-use them. Or delete them if they're not relevant for you. They were just examples that were auto-installed by default.

2. You need to edit that in the appropriate language file.
The fast way to find out which specific file to edit is by using the Developers Toolkit in your Admin:
http://www.zen-cart.com/content.php?...-files-to-edit
http://www.zen-cart.com/content.php?...lopers-toolkit