Kia sephia 1993 when i should to change oil of the motor

Manufacturers vary on intervals recommended. However, the old rule is the best rule....change your oil and filter every 3,000-4,000 miles. If using synthetic (common ones available in stores) that interval can be extended to 4,000 to 5,000. More exotic synthetics (such as Amsoil, using their filter) run to 5,000 miles and replace filter and oil lost during filter change. Replace all oil at 10,000. Actually a good deal even though the oil runs about $10.00 per quart.

Just buy new oil and Chang filter