Find the file addons/stock/report/report_deliveryslip.xml in your odoo base installation directory.
Copy the file to where you keep your customisations & additions, and a spare place to retain the original for reference.
Edit the file to your preferences. This requires care, as the QWeb syntax is obscure, coding in XML is tricky.
Copy the file back to addons/stock/report/ overwriting the base install one, perhaps using a script, so it is repeatable.
This is a concise subset of what a custom module does when overwriting base functionality.
Run this command to refresh your changed XML in the stock module only, to the database (which stores code as well as data)
./odoo-bin shell -d (your odoo database name) --update=stock
Restart odoo to activate your changes.
Answer applies to v10. Upvote this answer if it resolves your issue. Comment clearly if it does not.