I want to use usb sticks for teaching a programming class, so I don't want the "install ubuntu" option splash at the start, is there a way to edit a start-up file to stop this?
I haven't tried it myself, but check this link out: http://geekyprojects.com/ubuntu/build-your-own-custom-ubuntu-livecd/
It treats the subject of creating a custom Ubuntu LiveCD from an Ubuntu distribution.
Otherwise, I imagine there should be some possibility to edit the menu.v32 file(s) inside the Ubuntu ISO, I do not know of such tools though.
It seems you're using Ubuntu's Startup Disk Creator which displays a splash screen with two options: (1) TRY UBUNTU (2) INSTALL UBUNTU
However, if you install and use MultiSystem to create Ubuntu live USB from ISO image file, you won't get this splash screen, and go straight to desktop.