For deleting a transaction from your portfolio please perform the following steps.
Go to the page of the coin you'd like to delete transaction on
Select the portfolio under the Holdings tab
Click the transaction
Click Delete
Confirm
On the Website, choose Portfolio, click on Transactions, then choose the transaction you want to delete and click on 3 dots button on the right of it. Click Delete.
Please note that you can only delete transactions which have been manually added by you.