To edit an image first select it.
A selected image
Drag either of the images corner manipulators( 
) to change the corners or ends.
Drag any rotate manipulator 
to rotate the image.
Drag any scale manipulator
to re-size the image.
Drag the image to move it.
Image Properties Dialog
You can also edit the parameters of the image using its Properties Panel as shown below. To view the properties panel first select it.Then right-click on it, then select Properties Panel from the context menu that opens.
Image Properties Dialog
X
The X coordinate of the center of the image.
Y
The Y coordinate of the center of the image
Width
The width of the image.
Height
The height of the image
Load Image
Click the 
button to load a different image.
Layer
Use this drop-down to set the layer for the image.