You will need to hit a specific key during the POST (power on self test). This varies from motherboard to motherboard but us usually F1 or Esc. Often you see a message telling you to Hit ??? to enter Setup. You'll be presented with a menu of options. You will need to know what you want to change, select the desired option and escape selecting the option to change your changes. The PC will then reboot. It's good to have a goal before doing this.
How do I go about changing the BIOS?

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