If you install development desktop software, you could refer document "C:\Program Files\Bosch Sensortec\Development Desktop 2.0\DD2.0_BNOxxx.pdf" to upgrade BNO055 firmware.
The firemware could be download from https://www.bosch-sensortec.com/software-tools/tools/development-desktop-software/
Thank you very much for your reply.
We're actually working with Adafruit evaluation boards. Does your solution only apply to the official Bosch Application Board and BNO055 Shuttle Boards? Is there a documented way to upgrade Adafruit BNO055 and similar boards through I2C? Thank you for your time.