If a judgment of Legal Separation was already signed, filed and entered, you need to start all over to get a divorce from your spouse, i.e., file a new case requesting dissolution of your marriage. A judgment of legal separation cannot be amended to dissolve the marriage.
Please note that this answer does not constitute legal advice, and should not be relied on, as each situation is fact specific, and it is not possible to evaluate a legal problem without a comprehensive consultation and review of all the facts and court pleadings filed in the case. This answer does not create an attorney-client relationship.
You cannot amend your Separation Judgment to become divorced - you do need to start the process over with a Marital Dissolution Petition. If the Separation had not gone to Judgment, then you could have amended that filing. Now you will need a new filing (with a filing fee of $395 to the clerk for each of you), with new disclosures, and then you will be able to obtain a divorce with a Stipulated Judgment or a default. For the sake of both of your participating in the case, I would recommend a Stipulated Judgment. If you are both moving promptly on this, you could have your signed Judgment of divorce back in roughly 30 days, but you will not be single again until 6 months from the service of the Summons and Petition or from the filing of the Response. You can either process these papers on your own, or with the help of a paralegal, or with a lawyer.