Canon added the ability to upgrade the firmware on all it's lenses starting sometime in 2012. Cameras produced after that date have two categories for firmware updates: Camera or Lens.
The 1D X, 5D Mark III, and 650D/T4i were the first cameras to have this option. If you have an older camera, or older lens, you won't see the option for lens firmware upgrade.
The update is done exactly the same way the camera firmware update is done, but you also need a newer camera in order to do the firmware update.
If you know of any other updated lenses, post them here and I will try to post a link to the firmware.
Here are the links to lenses with downloadable firmware updates so far :
EF 200-400mm f/4L IS USM Extender 1.4x https://www.usa.canon.com …subtab=downloads-firmware
Firmware Version 1.1.0 corrects a phenomenon in which the subject may not be in focus on some occasions when
using this lens with some camera models (*) and performing AF shooting from approximately 3m.
* Some camera models: EOS-1D X, Mark II, EOS-1D X, EOS-1D C, EOS 5Ds, EOS 5Ds R, EOS 5D Mark IV, EOS 5D Mark III
EF 40 STM https://www.usa.canon.com …-2-8-stm?subtab=downloads
Firmware Version 1.2.0 corrects an issue if pressure is applied to the lens barrel while the lens is mounted to the camera (pressure can be applied even while attaching the lens cap while carrying the camera with the lens attached in a bag), the autofocusing function of the lens may stop working.
EF-S 55-250 STM https://www.usa.canon.com …subtab=downloads-firmware
Firmware Version 1.0.3 improves the autofocus speed when the EF-S 55-250mm f/4-5.6 IS STM is attached to the EOS M3.
EF 24-105 USM II https://www.usa.canon.com …subtab=downloads-firmware
firmware 1.0.4 enhances the effects of image stabilization when using the EF24-105mm F4L IS II USM with the EOS 5D Mark IV at a shutter speed between 1/100 sec. and 1/160 sec.
firmware 2.0.0 incorporates support for the "panning" scene mode with the EOS M5/EOS M6 has been added. The Panning scene mode reduces subject blurring and blurs the background when the lens is mounted to the EOS M5/EOS M6.
New firmware for these EF-M lenses incorporates support for the "Dual Sensing IS" function with the EOS M50:
EF-M 55-200mm f/4.5-6.3 IS STM https://www.usa.canon.com …subtab=downloads-firmware
EF-M 15-45mm f/3.5-6.3 IS STM https://www.usa.canon.com …subtab=downloads-firmware
EF-M 18-150mm f/3.5-6.3 IS STM https://www.usa.canon.com …subtab=downloads-firmware