You can quickly and easily change a forms button from "Submit" to any other word. Here is how:
Go to the Marketing Activities area.
Select your form and click Edit Form. 
Select the button and change the Label. 

 

Notice you can also change the Waiting Label. This is the text that is displayed after the button is clicked and before the form submit action is finished.

 

Click FINISH.
Click APPROVE AND CLOSE.

Bam!