TOPIC: How to change the "Next Step" button?

I know there is probably a simple coding answer for this - but I would like to change the "Next Step" button to be bigger, or a contrasting color, or just to stand out more (see attached screenshot). How can I do this?

I can upload my own button image, I just don't know what to change in the code of DT donate to make it appear.

This is styled by your template, not by DT Donate. Check your template CSS file for something like this:

button, html input[type="button"], input[type="reset"], input[type="submit"]