The Vivitar is a condenser enlarger. Even with the color head you need to use the condenser lens. To remove the socket on mine you back out two thumb screws and rotate the socket about 1/8 of a turn and remove from the rear. You might need to rotate the head to get the socket to clear the collum. Then you replace the socket with a plastic plug that you shuld have with the enlarger if you got all the parts.
I get beter results with the B&W head and mulit grade filters than I ever did with the color head.