Hi Michelle,
If it's Forms 2.0 you're using, you can drag the button. Unfortunately, that's not a precise way to do anything - but it's the only way Marketo currently allows you to do it.
Alternatively, and the way I would recommend addressing this, is to manually position the button with CSS (this can be done in the first page of the Forms 2.0 wizard, by clicking the cog/settings button when looking at themes).