How do you replace a oil pump VOLVO 850 97?

To replace the oil pump on a 1997 Volvo 850, first ensure the engine is cool and disconnect the battery. Drain the engine oil and remove the oil pan by unbolting it, taking care not to damage the gasket. Once the oil pan is off, unbolt the oil pump from the engine block and replace it with the new pump, ensuring proper alignment. Reassemble in reverse order, replace the oil pan gasket, refill with oil, and reconnect the battery.