You can find the Marlin for this Upgrade already prepared by Imre Horváth in his youtube vídeo about the topic. https://www.youtube.com/watch?app=desktop&v=G186YTCtpMU

If you don't want to change the electronics you will need to use both screens.

But you can cover the original one with the pieces I desing. You will have to make 4 holes in the original frame ( remove the anycubic screen previously or you can damage it) or you could glue the piece to the frame with construction adhesive.

Fin attach a PDF with the connections you need to make, it will be easier than the video of Imre Horváth. You will need 

4 x M3x10 Screws

4 x M3x12 Screws (if you drill the frame)

4 M3 Locknuts  (if you drill the frame)

And some dupont Conectors, or you could use jumper wires, you I recomned to use dupont and cut cables to length for a proper conection.