Slowly but surely, Huawei keeps working on updates to Android 6.0 Marshmallow for its devices. And now it's reached the Ascend Mate7 from 2014.
The company is currently looking for eager people to beta test the new software on their Mate7 units. There are some prerequisites before you can apply, though. First off, your Mate7 needs to be either the MT7-L09 model or the MT7-TL10 to qualify. You should also back up all your data before you install the Marshmallow beta, because things can always go wrong in such instances.
If you're fine with that and are willing to test the upcoming release, you have until January 22 to send an email to email@example.com which has to include your phone's IMEI number (which you can find out by dialing *#06#), as well as your current firmware version (listed in the About phone part of Settings). That's it. If you're lucky you'll be among the chosen ones who will get to play with the Android 6.0 update before it rolls out to everybody.
Thanks for the tip, Muhammad Idrees!