That depends on your machine, its not a function of windows.
When the machine starts look for a message that says "Press (some key or
other) to go into setup" or similar. If you see something like this, press
the (some key or other) it tells you to press.
Common hotkeys are F1, Del, F2, F12, TAB... but it depends on your computer
hardware.
There are many ways, depending upon your BIOS and manufacturer.
Sometimes ESC, F2, DEL or F12 will get you in. Just press tone right
after you see text appear on your screen after you power up your
system. Try each one..one will get you in. If not, press ESC and hold
it. That should cause a keyboard error and the system should offer to
let you into the BIOS.
