Put a Compact Flash card in the camera and format the card so it is devoid of data or images. Remove the Compact Flash card from the camera and put it in a card reader, attached to the computer. Copy the firmware update to the root directory (top level) of the Compact Flash card. You should see a folder called DCIM with the firmware update file sitting alongside it.
Eject the card from the computer and put it back into the camera. Connect the camera to the mains converter for power or use a freshly charged battery. (Power loss during updating may disable the camera.) Find the Firmware version section in the Menu. During the update process you will see a progress bar.
You will find the latest firmware update downloads and full installation details on the canon website.
On a 64-bit operating system, the drivers of the sound device must be 64-bit.
Device Manager can also try and update the drivers for you itself, and Windows users are strongly recommended to try this update facility as a first step - see Extra help for Windows users below.
Once you have the necessary information about your sound device, you can normally obtain appropriate updated drivers specific to your hardware from the internet.
If you use an EOS 30D, then you have two ways to update your firmware.
You can use the procedure described, or you can connect the camera to the computer with a USB cable and then use EOS Utility to update the firmware.