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.
In this step, be careful not to remove the headphone jack without first separating the top microphone from the upper case, as they are connected by a fragile flex cable.
Use a plastic opening tool to start to pry the headphone jack out of its recess in the rear case.
Then use the opening tool to gently peel the microphone up from the adhesive securing it to the top of the rear case.
Remove the headphone jack assembly from the rear case, being careful not to tear the microphone flex cable.
If you are replacing the headphone jack cable, use the edge of a plastic opening tool to remove the steel brackets for the volume buttons and the silent switch.
Transfer these steel brackets to the new headphone jack cable.