CS1525 unexpected symbol thisTranslate

I had a class a few semesters ago over C#, and I remember most of it, but I'm not at all sure what's going on here. I'm trying to make a 2D character jump when the Space bar is pressed.

 // Update is called once per frame
 void Update () {
                    //Transform variable for the object we want moved, and float to modulate the speed.
          Transform thisTransform;
          float f_Speed = 5;
       //If the Space bar is pressed, Translate thisTransformation upwards on Vector2. 
       if (Input.GetKeyDown (KeyCode = Space){
                thisTransform.Translate (Vector2.up / f_Speed)
                 }
 }