Remove the Bowden tube from the hotend or the extruder assembly.

Remove the blue plastic clip from the push fitting.

Push down on the grey part of the push fitting and simultaneously pull on the bowden tube.

You can also do this with the bigger fitting on the hotend, if you want to reuse your tubing, but I wouldn't recommend it since most hotends come with tubing anyways and the old tubing will most likely have degraded from the heating cycles.