You will need to remove the keyboard and palmrest screws, which require the use of a Torx T8 or flathead screwdriver.

If your N400c or N410c still has this screw, then you must use a screwdriver of the aforementioned Torx size.

If you find any Philip head screws holding the keyboard and/or palmrest in place instead of the Torx ones, then the system most likely had those screws replaced at one point in time.