You will need to head to the My Account section, find the Trading account you would like to remove and click/tap on view.

Next, you will be on the Trading account view. 

 Click/Tap on the three dots near the account ID.

Click/Tap the Delete account button.

 A notification will pop up asking for you to confirm the removal of the account.

This is an irreversible action. You will also not be able to remove an account with a negative balance until the account/s have been brought back to a Zero balance.

Click/Tap Delete Account on the pop up (or click No thanks to cancel)

A notification will pop up confirming the removal of the account.