What do you mean by boot option? If you mean setting in your UEFI/BIOS, immediately after hitting the power button, hit the F2 key or Del key Depending upon model computer, and look for BIOS Boot options if you want to boot off of USB. Note that on some laptops, you have to enable a administrator password in EFI/BIOS, and if you do that, Make sure you store the password, this is incredibly important that you write it down and don't lose it, or use a very common one that you can guess. Once that is done, grayed out options may appear. On some laptops, hitting the F12 or F8 key repeatedly during power on self test (POST, what happens when you power on) will get you into a boot options menu. It is also possible sometimes you need to try a different USB port for the bootable media. If you don't succeed, remember that there is always the external USB to drive adapter you can buy, once you remove the drive (if this is something that requires that), you can access it, you won't be installing on it, but accessing...
