What is difference between changing magnetic field and changing magnetic flux?
Magnetic flux is defined as:



Magnetic Flux takes in three parameters - Magnetic field strength, area, angle between the field lines and normal to that area.

Changing magnetic field specifically means either your magnetic field strength should change or it's direction with selected reference frame should change.

However a flux can change when either magnetic field changes, the area under consideration changes or the angle between field and area component changes. It might happen that two components are changing simultaneously but the flux is remaining constant so be aware of that.