Adding new inputs couldn't be easier. Just navigate to the app that you want to add inputs to and click "Browse" or "Add inputs" in the upper right hand corner of the screen.
There are two ways to delete inputs in Portal.
Just navigate to the "three dots" icon and select "Delete Input"
Click the check box to select and image and then click the "Delete Inputs" button at the bottom of the screen.
You can add metadata to images directly from explorer. Just click on a single image and navigate to the metadata window at the bottom right hand corner of your screen. Enter your metadata in JSON format and click anywhere outside the metadata window. The new metadata will automatically be applied to your image.