Hello @lisacole1,
Thanks for writing in! Regretfully there isn’t any setting to adjust the images in the single portfolio items. Since you have inserted the images in the portfolio item descriptions as well, you can simply hide the featured image instead. You need to add CSS code into X > Theme Options > CSS .
You need to use the Google Chrome Developer Toolbar to check the live HTML code and find which CSS selector of the featured image you need to use.
The featured image has entry-featured class while the body of the single portfolio item uses single-x-portfolio, therefore a proper CSS selector to hide the featured image in the single portfolio item page will be:
.single-x-portfolio .entry-featured {
display: none;
}
Here are some related links for further reading, this could help you in finding and implementing some CSS fixes: