Upgrading from 2.1.2 to 2.1.3
Before performing an update you should take your site offline by replacing the index.php file with a static one.
Step 1: Update your CodeIgniter files
Replace all files and directories in your "system" folder and replace your index.php file. If any modifications were made to your index.php they will need to be made fresh in this new one.
Note: If you have any custom developed files in these folders please make copies of them first.