Source Radius Not Affecting The Shadow

Im a new beginner to unreal engine 5
And Ive got a problem here I was watching a tutorial in Youtube and they say that I can make the shadow softer by changing source radius but in my screen even I change the source radius nothing happens to the shadow meanwhile the object is becoming somekinda wierd

This one before I change source radius

This one after I change source radius

Please help me. Thank You