The quick and easy way is to remove the <p> tags from around your heading. Rewrite the code as below:
<div align="center" class="style15 style16">
www .HannahandRhettswedding .co .uk
I've added spaces to the address so it doesn't change into a "click here" on the forum. Also I have removed style14 from the code since it only specifies a font-size which is overwritten in style15 anyway.
The site has obviously been written for a high resolution screen and the use of absolute positioning means that the whole of the page will not be visible on smaller screens or if the browser window is resized but that's not the immediate problem.