Use an iPod opening tool to slightly lift the top edge of the Wi-Fi antenna away from the logic board.
Use the tip of a spudger to pull the Wi-Fi retaining clips away from the inner frame.
Remove the Wi-Fi antenna from the iPhone. Make sure you don't lose the metal clips on the top of the cover where the 4.8mm screw attaches or the 4.8mm screw. That's the primary reason for abnormal Wi-Fi performance after the reassembly.