How to change text ONLY in Checkout Step 5?

Using v.2.0. and need to change the text ONLY that appears in the checkout 'Step 5: Payment Method' section that reads 'Add Comments To Your Order' above the text box. But I do NOT want to affect the same text that appears in Step 4 and only need to edit the same text within Step 5. How can this be done?

Might not worth the efforts, because you need to add a text plus a variable to controller and template. And all this only to change the text above comment textarea?