PHP extensions like Zend OPCache (former Zend Optimizer) and ionCube Loader are already pre-installed on all hosting plans at Hostinger.
To enable them, just open Hosting → Manage → PHP Configurations page. There, open PHP extensions tab and add checkboxes for:
ioncube_loader to enable ionCube Loader
opcache to enable Zend OPCache
Don't forget to save changes at the bottom of the page.
NOTE: