Get into the BIOS by pressing the Novo button on the laptop, just near the power button. You can use the Novo button only after you shutdown the laptop.
Once in, you will get a menu with the devices available for booting. Clicking on anyone of them will not start the image / Live CD on those devices. To do that, you must press Tab and then go to the BIOS. There, you will find option called Security.
In Security, you will find that cursor does not go to the Secure Boot at all. To enable it, you need to set up an Administrator password first. After that, you can change the password and disable Secure Boot.