Different communities have different customs and slightly different versions of the Kaddish. Find out from your rabbi (or a synagogue regular) what the customs are and what version of the Kaddish they use. Our Kaddish Tutor allows you to learn the Kaddish in more than one version. With time, we plan to add even more versions.
Of course, if you have a particular heritage, you should honor that by saying Kaddish according to that tradition. You don't have to change your version of the Kaddish for the congregation—unless you're the one leading the prayers.