Just connect your Lytro camera to your computer.

Lytro Desktop will launch automatically, and after any new pictures have been imported, you will be prompted to update if your camera is eligible for a firmware upgrade:

IMPORTANT: 

• You will not be prompted to update your camera's firmware unless all of the following are true:
• You are running the latest Lytro Desktop software version. (If you need help, see our Lytro Desktop update instructions.)
• Your Lytro camera has at least a 40%+ battery charge, and is connected to your computer via USB cable.
• The firmware update is being offered to all cameras.  Sometimes we may offer new firmware updates to a limited number of cameras initially.
• If you still cannot update to new firmware one full day after the date it was announced, please take the following steps, in order:
1. Shut down Lytro Desktop, and disconnect your camera.
2. Re-launch Lytro Desktop, and re-connect your camera.
3. Manually select "Check for Update" from the Lytro menu:
   
4. If still having issues after taking the above steps, please use the blue "Open a Support Ticket" link at the end of this article.