Your system restore is limited to the amount of space it uses, so when your computer is fairly new, the restore points will go back to when you first had it.
As more and more system points are created, more and more space is used -it is not unusual for system restore to take 10gb of hard drive space.
When it fills up, it deletes older restore points.
However, system restore should not delete nor restore files if that is what you are trying to do. It restores things like the computer registry, not files you have created.
What are you trying to do?