Flip the vacuum cleaner upside down so the wheels are more easily accessible.
Turn the screws in the center of the wheels clockwise to tighten them using a Phillips screwdriver. Ensure that the screws are snug before flipping the vacuum cleaner upright again.
Remove the old screws if they are stripped and refuse to tighten. Take the old screws with you to a hardware or home improvement store to purchase new ones of the same size and thread-type.
Thread the new screws through the center of the wheels by hand and ensure they do not cross-thread. Tighten them until they are snug using a Phillips screwdriver. Flip the vacuum cleaner upright.