Replacing the Base Shell Bottom Cover on Dell Inspiron N7110 17R laptop (part # WD05F)

I need to replace the Base Shell Bottom Cover on my Dell Inspiron N7110 17R laptop.  It is part # WD05F. I have the replacement base.  

I turned the laptop over and unscrewed all of the screws on the bottom thinking that the base would just lift off,  it did not.  I didn’t want to go any further because I was afraid that I might do damage to other parts.

What did I miss?  Are there other steps to replacing the base shell bottom cover?

Thanks for your help and suggestions.