There's a few options. The best probably is to set the style on those elements to use margin: auto;
margin-left: 50%;
margin-right: 50%;
margin: auto;
In the case of one of your images, for example, it would look something like this:
<img style='margin-left: 50%; margin-right: 50%; margin: auto;' src=... />
Of course, you should just put the css in a class and set the class of anything you want centered to that class. The css class would look like:
.centered {
margin-left: 50%;
margin-right: 50%;
margin: auto;
}