Help moving left side of Rect Transform

Having trouble finding an answer to this on the internet, maybe you guys can help me :)

I need a rect transfrom to move its "left" position. I say left because it is the child of another gui object, and its anchors are set to the outer edges of this object. Thus I cannot actually modify its 'x' or 'y' value directly. In this code, Bar is casted as a RectTransform, and increment is the distance I want it to move each frame.

 Bar.sizeDelta=new Vector2(Bar.localPosition.x-increment, Bar.localPosition.y);

this code is not what doing what I want it to do, How do I move ONLY the left side of this object (think expanding an image horizantally over time, but the image stays anchored to its 'right' position)?? Thanks!