Found it! Maybe it's a difference between Mac and PC. I'm on a Mac, and this is where I found it:
Go to Preferences (either the gear icon, or from the Mac menu bar.
Preferences>Invoice>Invoice Text
Then using the drop down menu next to "Invoice text items" you can select the item you need to change, and change it.
There really is no Preferences>Invoice Layout>Content -- at least on the version of ExpressInvoices on my Mac. But there is, after "unfocussing" my literal "following-of-orders", Preferences>Invoice>Invoice Text.