If by any reasons you want to delete your portfolio, then you need to disconnect all API keys from your portfolio and then you will be able to delete it.
1. Go to your portfolio and press edit icon.
2. Click on the cross icon near every exchange connected to your portfolio to disconnect them.
3. When there will be no connected exchanges left, the "Save" button will change to "Remove" button. Click the "Remove" button to delete your portfolio.