Please note you can only edit a draft invoice. If an invoice has been authorised, you will not be able to delete or make any changes.
Follow the steps below to edit a draft invoice: 
 -  Go to the dashboard
-  Click on 'Invoices'
- Click on 'Filter invoices' > 'Draft' (status) > Filter
-  Tap on the draft invoice you want to edit or delete. Click the edit button at the top right corner of screen
-  To delete simply click on 'remove invoice' 
-  To edit, make the required changes within the invoice, such as change date or edit the entries attached to the invoice and press save.