The term "Legal Separation" and "Dissolution" are distinctly different in that a legal separation does not result in dissolving the marriage itself, while a dissolution of marriage does indeed dissolve the marriage and will return the parties to their single status. There are several reasons why a spouse may want to file a petition for legal separation rather than a petition for dissolution of marriage. Some common reasons are because of the person's religious background, an interest to maintain certain healthcare benefits, or perhaps because the parties do not qualify to file for divorce because they have not met the residency requirement (there is no residency requirement to file a petition for legal separation in California).
If you initially filed for a legal separation for one of the reasons listed above or for any other reason, but you decide that would prefer a divorce, then you will need to convert your case into one for divorce. In California, you are able to convert your legal separation to a divorce at any point during the legal process, even after your legal separation is final. Either spouse can be the one to request that the legal separation be converted into a dissolution of marriage.
If a judgment of legal separation has not yet been obtained (meaning that you have filed your petition for legal separation but the proceedings are still pending) and your spouse has not yet responded to your petition, then so long as the residency requirement is met, you (the Petitioner) can simply file an amended petition and check the box for "Dissolution of Marriage". Your spouse will need to be served again with the amended Petition. However, if a judgment of legal separation has not yet been obtained but your spouse has already filed his or her Response to your original Petition for Legal Separation, then you may need to request approval from the Court.
If a judgment of legal separation has already been obtained from the court and you later decide that you would prefer a divorce, then you cannot just file an amended petition. Instead, you will need to start over with a new case by filing a petition for dissolution of marriage and pay the filing fee again.
Regardless of the status of the petition for legal separation, either spouse can petition the Court for dissolution of marriage. Because of this, it is typically better to simply petition for dissolution of marriage from the get-go unless both parties agree to the legal separation or a legal separation would benefit one or both parties. Also, it is important to keep in mind that the six month waiting period to be returned to single status does not start ticking until the Petition for Dissolution of Marriage has been served on the Respondent, despite the status of the petition for legal separation.