How to reduce the size of the File System

We're in the On-Demand environment and the Sugar Insights shows our File system Size is 90% of the allocation and the Database size is 61% of the allocation.

The Database size has been reduced in recent months because of our clean-up project (deleting very old and no longer useful records).  The File System size continues to grow.

What can be done to reduce the size of the File System?