Once they have been deleted, you can not do anything with them. They do not exist. You can forward them to email if you have that service, select Forward after reading the text, select the contact you want it to go to and if you have the email address programed, select that option. Depends on your phone and you services.
You have to contact the Subpoena Compliance Group at 800-877-7330 and choose option 3. They will send you a form that you must get notarized stating that you are the account holder. They will only send you the text message detail (phone numbers and dates and times) for the previous 90 days but not the content of the texts. Good luck!
Check out a fun infographic that teaches you how to increase storage, enhance security, improve battery life and clean your device.