For deleting a coin from portfolio you have 2 options.
1. First one for keeping your history is to create a Sell transaction for your coin which will make the amount you hold as 0.
2. For the other option please follow below steps:
- Choose the coin and click on it.
- Then click on the transaction under the Holdings tab.
- You'll see the Delete button, click on it too.
- Confirm (Yes).