How Defragmenting Works
The solution is to defragment the disk. Disk defragmentation takes all the pieces of each file, and stores them in one place. It also makes sure programs are each in one place, and that unused space on the hard disk is all together.
Defragmenting a disk is like sorting and arranging items in a storage room; boxes holding similar things are combined, and all the boxes in the room are stacked neatly to create more space. Defragmenting does not change any of the files' contents, and does not affect anything you see on the screen (documents, shortcuts on the desktop, etc.)
If you'd like to learn how to defragment manually, click here.