how to change lidar point num?

I select one vehicle in vehicles library , this vehicle have one lidar, one camera....
when I receve the lidar data with `PythonAPI` , I found the point cloud only have 20,000 points, but I want to have 10,000 points per point cloud.  
So , I change the `LaserCount` from 32 to 64 , but the points num is not change .
Does anyone know how to change that?
thanks ~