We've changed the battery,still does not turn the light on/off.
It does turn the fan on.
What could be wrong?

Um, maybe a little help here. We cannot see through our computers.
What is the remote?
Is this a ceiling fan with a light?

Hey there,

Maybe a dip switch problem. Did you try changing the batteries too?

Check this remote control troubleshooting guide - it has a step by step portion for troubleshooting your remote issue. Let me know if it was helpful