1. Log into WHM (Root Panel, not Domain Panel).
2. Under 'Software' section, click on 'EasyApache' (Apache Update) link.
3. Ensure 'Previously Saved Config' is selected and click the Start customizing based on profile button.
4. Keep clicking Next, until you reach the 'Short Options List' page and scroll to the bottom of the page.
5. Click on the 'Exhaustive Options List' button.
6. Scroll down to the PHP section and find MySQL “Improved” extension.
7. Ensure the check box is filled in and scroll to the bottom.
8. Click the Save only button.
9. On the next page, click the 'Build profile I just saved' button.
10. A pop box will appear and ask you to recompile Apache and PHP, select Yes and I understand.
11. Wait until the Build ouput is complete and the MySQLi extension should now be installed.