You need to start with an invoice template and use a CSS transform to change the title, something like this would work.
.transform-invTypeName1 {
content:"HIRE<br/>AGREEMENT";
}
Once you have the invoice template looking exactly how you want, you then need to name it so it includes the text delnote and then add that template path as the default delivery note template in the advanced features section.
We have some additional guidance on this process here: