Information about the availability of firmware updates can be found under Downloads section of your camera model support page
If a firmware update is available, there will be steps on how to install the firmware for your product and also instructions on how to check the firmware version.
If you cannot find a firmware update listed under the Downloads section, it just means that Sony is currently not offering a newer firmware.
Get notified about firmware updates, products alerts and more with the Support By Sony app.
You can learn how to update your camera firmware with this video tutorial:
How To: Update your Sony Camera Firmware on a Windows computer