First of all let’s see what BIOS is. After all, most users don’t need to deal with that. To put it simply, BIOS is a program stored in the motherboard that is responsible for the hardware and software interaction. All settings are stored in non-volatile memory and are not erased due to the built-in battery. That is the reason why settings may reset every time the computer is turned off – it usually happens when the battery is low (usually it works for several years).
Well, how to enter BIOS configuration:
In the vast majority of desktop computers as well as laptops BIOS can be entered by pressing the DEL key early in the boot. Usually, during the booting some additional information appears on the screen: something like «Press DEL to run setup» or similar. Some PC and laptop manufacturers don’t stick to this rule, so BIOS can be entered by pressing some other keys. Since you haven’t specified your laptop manufacturer – here are the most popular alternatives: F2, F9, F10 and F12.

Sometimes the tip which keys you should press is written on the screen during the boot, sometimes not. If neither of these keys work, it would be better for you to read the laptop instruction. Or you may ask a question here, we are always ready to help you.
How to change the boot order in BIOS:
Find «Boot» or «Boot device priority» in the menu. Sometimes this section can be found in the root menu, sometimes it can be hidden inside one of the items (usually inside the second or third tab). In general you should be able to find three menu items: 1st boot device, 2nd boot device, 3rd boot device.

In the first tab - specify the DVD drive, in the second - system hard drive. These settings are revertible, but there is no practical need to do that – if there is no disc in the drive, the download will start immediately from the hard disk