Alternatively, look for a 'Press F10 for boot options' or similar as your computer is starting to bring up a list of drives.
To make a USB drive bootable, you will need a utility such as Rufus or Unetbootin.
For this reason, it's worth checking whether you really need to update your BIOS.
Most update packages consist of a flash program which is responsible for the setup and the actual BIOS-Update, often accompanied by a text file of some sort detailing the release notes.
At this point, it's well worth reading any instructions on the manufacturer's website about the exact updating process for your BIOS.
Even if the BIOS update is designed to be run from a floppy disk you can usually use a USB flash drive, but you may need to first enter the BIOS to tell it to boot from the CD or USB drive instead of the hard drive.
Typically you won't need to as a PC or laptop will be set up to look for a removable disc or drive before trying to boot from the hard drive.
They do vary, and you may need to configure some things before starting the update process, such as disabling secure boot modes and fast boot modes.