Drupal has language files that hold all of the messages and labels you see while using your site. You can change this text if you need to.
To change language used in Drupal, you need to translate the language strings that come in the Drupal distribution. Drupal comes bundled with a module called Locale that will let you do that, but it's really rather complicated. There's a much simpler module called String Overrides that will let you change a few things with a few simple steps.
Step 1. Download and install the String Overrides module
Download and install the String Overrides module. You can get it from http://drupal.org/project/stringoverrides.
After downloading go to Modules then Add New and use the Browse to locate the file for upload. Click Install.
Check the Enabled boxes for both String Overrides boxes and then click Save configuration.
Step 2. Access the module from the Configuration menu
Click Configuration and then click Translate Interface.
Step 3. Make the change
Type the exact phrase you want to change on left and the replacement phrase on the right. Click Save Configuration.
You can add extra rows and make multiple changes at one time.
You can see the original phrase in the image above and you can see your new phrase in the image below:
This is great for quick and easy changes to the basic language. If you are going to do a complete translation to another language or revamp every single language string, you are better off using the Locale module that comes bundled with Drupal core. It requires some advanced knowledge to use. For smaller changes, localize and personalize your site the easy way with String Overrides.