how often should i change my transmission fluid ? on 2003 Kia Spectra

Could i need to change my transmission fluid if it is slipping ?

Asked by for the 2003 Kia Spectra
The transmission may already have internal damage if it slipping but servicing the transmission would be worth trying if it is the oil that has broken down. I would change transmission oil every 30k miles. Kia as a car manufacturer put a lot of great technical information and work shop manuals on line for free for Kia owners.