Firmware Upgrade:
In order to upload version 6.51 to a device running a firmware version below 6.50, you need to upgrade first to version 6.50, since older firmware versions do not support firmware file decryption.
Firmware Downgrade:
In case a firmware must be downgraded from a device with firmware 6.51 or higher installed, the downgrade is only possible via firmware 6.50 with an updated signature.
Please also check the Release Notes attached for more detailed information.