Left click the existing text and an "inline text editor" will appear.  Make the adjustments to the text and click "Save".

The wide format slideshow displays text and an image in adjacent 'columns' on the page, with a navigation element to move from one slide to the next.

The image should be 450px wide (wider images can be used, but they will be 'squashed' to a 450px width - and probably lose viewing quality as a result).