The Frame Editor allows exact resizing and positioning of frames on the canvas.
Select any frame on the canvas, or multiple frames, and click on the border portion of the Toolbox to launch the Frame Editor.
The Position and Size options are located at the bottom of the editor.

The X & Y parameters specify the position of the selected frames on the canvas.
Multiple select frames to line them up precisely along either of these axes.

The width and height options specify the frame size.
Multiple select frames to create identical widths and/or heights.
 
The Angle control rotates the entire frame. To rotate the image within the frame, use the Image Editor control.