Please note that C6 is no longer supported in macOS Catalina and later.
For more information, please read this.
UPDATING DEVICE OS WITH C6
Go to https://www.elektron.se/support/ and select your machine from the drop-down list
Download the latest OS and the C6 software
Install C6 on your computer
Make sure your machine is connected via USB and set to USB-MIDI mode only under SYSTEM > USB CONFIG,
Start C6 on your computer, click the Config button to open the config screen. Make sure that the machine you want to update is selected under MIDI In and under MIDI Out (They will be marked blue when selected).
Drag and drop the .syx file containing the OS update to the C6 file list.
In the device GLOBAL/SETTINGS menu, navigate to SYSTEM, and then select OS UPGRADE, the display should read OS UPGRADE, WAITING FOR SYSEX.
In C6, click Send to start the os file transfer to your machine.
For more details about configuring the C6 software, see the manual included in the C6 download.
For further information about the OS upgrade, see the product manual, which can be downloaded from the same location as the OS update and the C6 software.