you mean the citation style? You have a very large number to choose from:
http://zotero.org/styles
but if that's not enough, see
http://www.zotero.org/support/dev/citation_styles/style_editing_step-by-step
No, I mean the design on the list of references. Anytime I add a reference the list of references is set back to som default style that I don't like. That is what I want to avoid. I want the list of references as I have designed it, but somehow word or zotero or maybe both seem to disagree with me.
You should be able to modify the style for "bibliography" in Word, which is what Zotero applies when it inserts or updates the bibliography. Details depend on your Word version, but should be quick to google.
http://zotero.org/styles
but if that's not enough, see
http://www.zotero.org/support/dev/citation_styles/style_editing_step-by-step