You can modify the displayed images/logos of the app and the Portfolio Manager.
Open the Portfolio Manager > click on the 'Settings'-icon in the top menu >
choose 'General Settings' > click on 'Branding':
You can drag and drop the image to the relevant input field straight away or click on it, to search for the file you want to upload.
The format and maximum size for each image is mentioned at the right side of the input field.