Image won't stay centered

Good morning to all,

I know this has been posted over and over (I’ve looked at most:)

And, I guess it has to do with my theme, but I can’t get an image to stay centered when I publish.

Here’s a link to the page in question: http://money-blogging.com/279-2/

I don’t really know how to add/delete code in the theme??

Here is the coding that I think has to do with it:

.alignright img, img.alignright
{
margin: 1em;
margin-right: 0;
}

.alignleft img, img.alignleft
{
margin: 1em;
margin-left: 0;
}

.aligncenter,
{
float: center;

Could someone walk me through what changes need to be made…I’ve had a few bad experiences trying to change things myself:)
Thanks