There are several different problems that could cause food residue to be redeposited on the dishes during the wash cycle. You could have a problem with water fill, water temperature, spray coverage or detergent. You could also have a problem in the sump area that could cause food to be redeposited on dishes.
Here are some troubleshooting tips:
Check the water fill level in your dishwasher. Allow the dishwasher to fill and then stop it by cracking open the door before the spray starts. Open the door and look at the water level in the tub. The water should be within 1/4" to just touching the bottom of the heating element. If it is not, then I recommend making sure that the water cut-off valve for the dishwasher is fully open. Cycle it shut and then back to the fully open position. You may need to shut off the water, disconnect power to the dishwasher and disconnect the water supply to check for proper pressure and flow from the supply line. Debris or deposits in the inlet water screen to the dishwasher can also inhibit flow.
Check the water temperature. Run the kitchen sink hot tap for 1 minute. Fill a glass with the water from the hot tap. Measure the temperature of the water with an accurate thermometer. You should measure at least 120 degrees. If not, then I recommend adjusting your hot water heater.
Use only fresh powdered dishwasher detergent in your dishwasher. Make sure that you use the proper amount. Keep this detergent in a cool and dry storage area. If the detergent is old and clumpy, it will not dissolve and clean properly.
Check your rinse aid dispenser. Make sure that you are using the proper amount of rinse aid according to the recommendations in your owner's manual.
Properly load the dishes to prevent nesting and blocking of spray patterns.
Make sure that your top rack is properly pushed in all of the way to properly engage the upper spray arm.
Check your spray arms for cracks, splits or deposits.
If these tips don't help resolve your problem, then you can disconnect power to the dishwasher and access the sump area to check for problems. The first image below shows the procedure for accessing the sump area down to the chopper blade assembly area. Check the filter screen for a tear as shown in the second image. Also, debris or labels on top of this filter screen can cause food particles to be redeposited on dishes. You can check chopper blade area for debris or paper labels that may be present. The third image shows a check valve that must be properly in place. If this check valve is damaged, it will need to be replaced.
A problem with the dishwasher drain could also cause food to be redeposited on dishes. Check your drain system to make sure that it complies with installation guidelines. Check the dishwasher drain hose where it attaches to the sink drain or garbage disposal. A build-up of grease in this drain hose could prevent the dishwasher from draining properly.
If these tips do not help you resolve this cleaning problem in your dishwasher, resubmit your question with additional details.