Use angled tweezers to grip the antenna's black coaxial connector, as close to the connector head as possible.

Gently lift straight up to disconnect the cable.

Be gentle when disconnecting the cable, as it's very easy to tear the socket from the motherboard.

Repeat the disconnection procedure on the white antenna cable.

To reattach coaxial connectors like these, align the connector over its socket and press down with the flat end of a spudger. The connector should snap into place. This can be tricky and may take a few tries.

During reassembly, make sure the antenna cables are in their groove on the edge of the phone.