An agreement can't be deleted once it has been signed. The button is not displayed in this case.
If you wish to no longer use an agreement once it has been signed, please refer to the pages about cancelling or suspending agreements.
On the agreement page, set your filter on prepared agreements. Once this is done, you can delete a prepared agreement using the delete button in the top-right corner It is also possible to select multiple prepared agreements to delete them in bulk.