Rotating images in Aperture is as simple as two clicks. Ill show you the simple steps needed so you can do it every time.
The first step is to find the rotate button. Its located in the toolbar at the top of your screen. Click either of the two on the right. You can also press on of the square brackets ( [ & ] ).
Notice the images in there slanty uncorrected position.
And after a click or 3 the image are the right way round. You don't have to change the tool to change the rotation of the image just keep clicking and the image will keep rotating.
Thats was a quick tutorial. There will be another one tommorow. You can read the rest of this series here.