iFixit

Be sure not to lose the small grounding finger for the rear facing camera near the power button. This finger rests on top of the PCB, screwed down, and covered with the adhesive black plastic tape.

Remove the 2.4 mm Phillips screw next to the headphone jack.

Use the edge of a plastic opening tool to peel the upper antenna off the headphone jack.

Use a pair of tweezers to remove the upper antenna from the iPhone.

Before reassembly, be sure to clean the metal-to-metal contact point on the upper antenna (not the mating halves of its connector) with a de-greaser such as windex or isopropyl alcohol. The oils on your fingers have the potential to cause wireless interference issues.