How to change machines on a nlkvm-4 kvm swtich

Question

Hi
I recently got my hands on a newlink nlkvm-4 4 port kvm switch that came to me without the user manual. I googled and found other kvm user guides but I could not find the newlink nlkvm-4 manual on line. I have 2 machines hooked up to it at the moment and have no idea how to switch from one to the other. Could anyone who has one let me know the function key sequence to switch and any other function key sequences that might be helpful to me.
Thanks
A