I also could not find any info on changing the line cord on this unit.
With luck someone else will jump in with some info.

I can give you some general info.

On 3 wire hookups the Neutral (white) and the earth ground (machine frame) are the same.
On 4 wire hookups Neutral and earth ground are separate.

In many units there is a wire (ground strap) that goes from the center connector (Neutral) (white) of the units terminal strip to the frame.
This ground strap has to be disconnected. Either totally remove it or disconnect it from the frame then tape up the connector end and zip tie it so that it cannot short to anything.
Then the new 4 wire is hooked up as below:
Red to where red was
Black to where black was.
White to Neutral usually the center terminal.
Green to the machine frame where the ground strap was connected.