When you want to modify a part of your Shop (that can't be changed in its layout using the Joomla template's CSS), you must know, which file you have to modify, to create the layout you want.

To quickly find the file, which produces the HTML output you're seeing, you can enable the DEBUG mode ("Admin" ⇒ "Configuration" ⇒ "Path & URL" ⇒ check "DEBUG?" and save.

After having done that, you will see blue info icons all over the Shop, which show the file name of the included file on mouseover.

The most changed files are