Bathroom sink drain replacement

[Amituofo]

Hi plumbing experts,
My bathroom sink drain is leaking. How do I remove the existing one and fix it? Please see the pictures below. There's no thread at the bottom for me to unscrew the drain.

 

[Marlinman]

The lower tailpiece and flange will screw off the top flange.

 

[Sponsor]

 

[Dj2]

Hold the flange inside the sink firmly and twist the drain tube under the sink to open.