It happens every few months. My operating system drive runs out of space, and I must begin the hunt for things to delete or move to another drive. As a first step using a cleanup utility such as CCleaner is helpful, but it only finds the easy targets such as temporary files. Unfortunately, deleting these files does not typically result in a major impact on free space. For the more difficult second step, I like to use storage space utilization tools to manually determine what I can delete or move.