I have to mention couple of things here before we get started.
- In version 3.1, we've updated the Paypal payment gateway system. It requires "Secret Key" now. So make sure to put your "Paypal Secret Key" on the payment settings for successful transaction. Same thing goes for instructors also.
- If your current version is not 3.0, you can not update your application to version 3.1. It will occur errors.

Update instructions from version 3.0 to 3.1 -
PLEASE READ AND FOLLOW THE STEPS VERY CAREFULLY.
Before starting, keep a backup of files and database of your running 3.0 version. So that there will be no fear of losing data.
1. First, Go to your application > config > database.php file. Keep a backup of the database.php. It will be needed after couple of steps.
2. Go to the folder update_pack and open the application folder. Copy all the files and folder inside application folder.
3. Replace the existing files and folder inside application folder with the copied application files and folder. Which you have copied on step 2.
4. Now put back the database.php file inside application > config. Which you have backed up on the first step.
5. Now, Go to the folder update_pack and open the assets folder. Copy all the files and folder inside assets folder.
6. Replace the existing files and folder inside assets folder with the copied assets files and folder. Which you have copied on step 5.
7. If you have done this so far, it's time to update the database. Go to the application's phpmyadmin and open the database.
6. Now, Go to the folder update_pack and open the SQL folder. Import the update_3.1.sql file. It will update your database.

That's it.
If you face any issue during updating the application to version 3.1. Let us know through ticket.