I can think of only two reasons why solar-powered lights would switch on during the day. One is some form of circuit failure. If that's the case, there's nothing you can do about it. (The components inside the lights are probably on a single chip. You can't repair a particular component without replacing the whole chip). The other (far more likely) possibility is that the light sensor (which detects when it's dark enough for the light to come on) is obstructed.
Examine the lights and try to identify where the sensor is placed. Then clean the area thoroughly and ensure that it hasn't got something like a leaf lying on top of it.
Chris