The Field Slideshow makes it easy to create a slideshow from just an image field.
With Fields in core for Drupal 7 we also got a more powerful display formatters for fields. Fields now ship with their own formatter settings forms and make it really easy to change the display of a field, and Field Slideshow really make use of this.
For more details check out the Field Slideshow project page.
The first thing you have to do is download Field Slideshow and place it into sites/all/module. Then go to Administration >> Modules and enable the module.