What you're looking for is exactly what R0J0hound mentioned.
Setting the origin point
If you double click on the collision sprite object, the image editor should open.
In the image editor, on the left-hand toolbar, choose the 2nd tool from the bottom (looks like a crosshair). This is the "Set origin and image points" tool.
With this tool selected you can set the origin point of your object wherever you want. You can also use the number-pad on your keyboard to quickly snap the origin point to the center edges or corners of the sprite image, though Num-Lock must be enabled for this.
If the default images of your sword and character face rightward, then for your collision sprite, you'll probably want to put the origin point on the far left edge. You can press numpad-4 to do this, if Num-Lock is enabled.
Accept the changes and then try it out in the editor by holding down Ctrl + Shift and Dragging one of the corner resize handles on your collision object. It should now scale around the new origin point you just set.
(You'll want to undo that resize afterwards of course. Be careful not to also undo the change to the origin point.)
Flipping the sprite
As for flipping or mirroring the object, in that object's actions, in the Appearance group, you can use the "Set Mirrored" action to flip the object horizontally, and the "Set Flipped" action to flip the object vertically.
C2 Manual Page on Image Points