Here are some simple steps to automate converting and image from one format to another.

1. Open the first image you want to convert.
2. In Photoshop go to ‘Window’=>’Actions’.
3. Click on the ‘Create new action’ button and give it a meaningful name, something like jpg2png will suffice.
4. Save the image you opened manually.
5. Once done, click on the stop button.
6. Go to ‘File’=>’Automate’=>’Batch’.
7. Under the ‘Actions’ drop down select the one you just created and click ‘Go’.