Images saved in OpenEXR format can be exported to either individual images, or a video sequence can be created, thus exr to png conversion is certainly possible. The best way to handle EXR format is to use exrtools bundle of utilities that offer plenty of ways to convert or edit these images. Nevertheless, other graphics software may also support EXR format and work with it.
Open EXR file Open PNG fileA set of tools for handling EXR images