Car seat covers can receive a lot of abuse over time. Children spill drinks and food on the covers, draw on them with markers and crayons, and infants can even spit up on their car seats. Although car seat covers can be washed, eventually you're probably going to have to replace them.
Buy a replacement car seat cover. Replacements are available from a variety of sources, including Graco and a number of boutique type shops offering different styles and design options. You need to know your car seat model number to order the correct replacement cover. You can find the model number on the plastic base of the seat or on the paperwork or warranty you received with the car seat.
Remove the car seat from car, completely unhooking all straps.
Undo the elastic and clips holding the car seat cover to its plastic frame so the straps are the only things holding the cover on the car seat.
Ease the bottom buckle back down through its designated hole in the car seat cover.
Flip the car seat over and follow the shoulder straps down to a metal buckle. Release the shoulder straps from the buckle by sliding them down and out through the small opening in the metal. Now pull the car seat cover loose of the straps. Once you have removed the cover, the straps should be sitting loose on the bottom of your car seat. Do not remove any of the car seat's pads.
Place the new cover on the car seat and run the straps and bottom buckle back up through the seat. Thread them through the bottom holes first and then through the corresponding top shoulder strap holes.
Run the shoulder straps back through the pads and reconnect them to the metal buckle.
Wrap the elastic edge of the new car seat cover firmly around the plastic car seat base. Attach any clips in the correct locations.