To disassemble laptop asus FX504 and replace wifi card, you need to unscrew all screws
on the bottom cover of laptop.
Use a plastic tool, to open laptop case.
In description of this video, you can find useful links to various laptop disassembly
tools and parts.
After removing bottom cover, disconnect battery connector from the motherboard.
Disconnect wifi antenna and unscrew one screw that holds Wi-Fi module.
In asus FX504 uses Wi-Fi card Intel 9560NGW Connect the battery connector to the motherboard.
Install bottom case of laptop and screw all screws in the order show on this video guide.