Go to https://config.qmk.fm/#/1upkeyboards/ select your PCB Model and layout. Modify your layout if desired then click COMPILE on the top right, wait until completed and click FIRMWARE to download the .HEX
Open QMK Toolbox and use it to Open the .HEX file
Plug in your keyboard while holding 'Spacebar + B' OR press the reset button on the backside of the PCB while plugged in to load DFU mode.
If autoflash is enabled in QMK toolbox you should see the firmware being installed as soon as the keyboard is recognized.
If autoflash is not enabled click “Flash” once the drivers have finished installing.