What are the right steps for divorce if we have a child and I have a temporary green card?

Sorry to learn you are contemplating a divorce. If you have exhausted steps, such as marriage counseling, to try to resuscitate your marriage, then you should consult with a local domestic relations/divorce attorney about your rights and obligations, especially those related to your child, in the event of a divorce. Regarding immigration, the holder of Conditional Resident status (sometimes called a temporary or 2-year Green Card) remains obligated to file a petition to remove conditions during the 90 day period before the end of two years of Conditional Resident status, and if the foreign national is divorced, then she may file the petition with a request to waive the usual requirement that both spouses file the application together. To be successful with that type of case, it will be important to have a particularly strong set of documentary evidence that the couple lived in a bona fide marriage notwithstanding that it ended in divorce - your child's birth certificate naming both parents is one example of such documentation. It would be wise for you to consult with an immigration attorney who, after learning all of the relevant details about you and your marriage, would be able to advise you of steps to take in anticipating of filing a petition to remove conditions with a request for a waiver, and who would be able to offer legal representation to you in that application process.