Photoshop is an imaging and design software. The following instructions may require slight revisions depending your computer's operating system (Mac or Windows).
Creating a Slide Using Photoshop
Modifying Dimensions of an Existing JPEG File
If you have an existing JPEG file that needs to be resized to the correct pixel size (1080 pixels), please refer to these instructions on how to modify the size of an image in Photoshop: How to Resize Images in Photoshop
Please note, however, that if time allows it is often best to adjust the image size using the software originally used to create the slide. For example, if you used PowerPoint to create the slide, use the original PowerPoint file to make adjustments and save it as a new file.
Modifying Dimensions of an Existing File
If you have an existing PDF file that needs to be reformatted as a JPEG, please refer to these instructions: How to Convert PDF to JPG using Photoshop