If you want to convert/format all image into same name (replacement) using ImageMagick then it is better to us the mogrify
command than convert
command.
Here is an example on how to use mogrify
command to convert all .png files into .jpg files mogrify -format jpg *.png
* Here is a link to ImageMagick documentation on basic usage, http://www.imagemagick.org/Usage/basics/.