The Send All New Firmware to K3 button is enabled only when there is new firmware available to send to the K3. All the required firmware files necessary to load the K3 must be present for the button to be enabled.
The Send All New Firmware to K3 and Send Checked Items to K3 buttons are disabled while copying files from Elecraft.
If the button is not enabled when newer versions are shown in the Available column, try selecting the Copy New Files from Elecraft Server into Local Folder check box and click Check Versions Now to copy the required files from the Elecraft server.
If the Send All New Firmware to K3 button is still disabled, required files may be missing from your Firmware folder. See Missing Files.