Although the answer depends on the specifics of your situation, if you are Catholic or plan to marry in a Catholic church, you likely will need to have your first marriage declared null. Depending on where you were married and whether you and/or your ex-spouse were baptized, the matter might be resolved rather simply, or it might take more examination and work.
As you prepare for your upcoming wedding, you have probably given a great deal of thought to the sacredness of marriage. It is that sacredness that the Church’s marriage policy strives to protect. But while the Church believes that a valid marriage cannot be dissolved except through death, it also recognizes that what appears to be a valid marriage is not always so. Please note that children of an annulled marriage are not considered illegitimate.
I urge you to contact your pastor or a Church pastoral minister and investigate whether your previous marriage might be declared null. You should also educate yourself about the annulment process and policies.