Michael on "Images in widget not centered"

I am using Ocean Mist theme, and the images in the widgets I added to my sidebar appear left-aligned instead of centered, despite center alignment being chosen from within the widget.

It seems like I can add to my style.css but I don't know how to edit the existing code. I have searched the forums and tried some solutions and none of them has fixed the issue.

Is there any code I can add to the stylesheet to resolve this? Also, I don't know how to tell which version of WordPress I am running. It doesn't appear in the source code for the website, and I can't see it displayed on the dahsboard anywhere.

Thanks for any help!

use:

#content img.aligncenter {
display: block;
margin: 0px auto;
}