submit forms javascript

How do I change the value of a Submit button in HTML / Javascript?
I am working on a page, depending on the situation, the value will Submit different. Basically ranging from "Please Click After completing the form" to "Save here. I know I am not explain much, but I need a basic principle to start. Is there a way I can do with just one: document.getElelmentByID (name_of_form "). submit.value?