A red circle with a number inside in the corner of the App Store icon on your iPad means that you have one or more app updates available. Here's how to find and install them.
Steps
Step 1. Click on the App Store icon on your iPad home page to launch this application
Step 2. Click on the Updates tab to see all available updates for the apps installed on your iPad
Each update listing assumes that it will take effect after download. Now click on the "Update" button.
Step 3. Next, you will be prompted for your iTunes password or email address and password
Enter them in the appropriate fields and click "OK".
Step 4. The application you are updating will be displayed in gray, and a status bar will appear on its icon
Various messages will be displayed under the icon until the update is complete, starting with “Waiting”, then “Loading” and finally “Installing”. When the status bar fills up and the app icon returns to normal, you can use your updated app.