Ray Cast Click on Enemy - Change Current Target

My raycast target enemy works perfect, my only problem is when I have a target the only way to untarget is to kill the enemy or to right click. I want to make it so if I have a target and i choose to click another one, the target will change. Cant figure it out!

 void Update () {
 
 
         if( Input.GetMouseButtonDown(0) && newon == true)
         {
 
             Ray ray = Camera.main.ScreenPointToRay( Input.mousePosition );
             RaycastHit $$anonymous$$t;
             
             if( Physics.Raycast( ray, out $$anonymous$$t,  100 ) )
             {
                 float distance = Vector3.Distance($$anonymous$$t.transform.position, transform.position);
 
                 
                 if(distance < 8) {
                 string $$anonymous$$tTag = $$anonymous$$t.transform.tag;
                 if ($$anonymous$$tTag == "enemy" && newon == true)
                 {
                 Debug.Log( $$anonymous$$t.transform.gameObject.name );
                 target = $$anonymous$$t.transform.gameObject;
                     SelectTarget();
                 }
                 }
 
             }
         }
 
 
         if (Input.GetMouseButtonDown (1)) {
                 DeselectTarget();
                 }