Earlier this week, Razer started pushing out the Android 8.1 Oreo update to its Razer Phone. And now, the company has made available kernel source code as well as factory image for the update as well.
The factory image weighs in at around 1.6GB. Complete instructions for flashing the factory image are available at the company's website (see General Instructions page link at the bottom).
Razer says you should not use the included USB Type-C to Type-C charging cable for flashing as it's meant for fast power delivery, not for data transfer.