After disconnecting the speaker from the headset, it is still connected by the wires that power the speaker itself.

With heat or with a sharp tool, remove the glue around the wires that connect the speaker to the headset.

Using the new speaker, you can reattach the wires soldering them in with existing glue.

If replacing internal components and NOT the speaker, you can do so without severing any wire connections; operate carefully to not sever them unnecessarily!