The simplest way to retrieve deleted files is to look for them in the Trash. Every time you delete a file, your Macintosh stores it in the Trash. To retrieve files stored in the Trash, do the following:
Right-click the Trash icon on the Dock and select Open. A Finder window appears, displaying the contents of the Trash.
Right-click any file stored in the Trash window. A pop-up menu appears.
Choose Put Back. Your chosen file returns back to the folder where it was stored before you deleted it. (You can also drag a file out of the Trash window and drop it in any folder you want.)
If you empty the Trash and accidentally throw out any files you might really need, you can buy a special utility program that can recover deleted files. Three popular disk utility programs that can recover deleted files are DiskWarrior (http://www.alsoft.com/), TechTool Pro (http://www.micromat.com/), and Drive Genius (http://www.prosofteng.com/).
If you're sure you want to delete files for good, empty the Trash, which frees up space on your hard disk. To empty the Trash, right-click the Trash icon on the Dock and select Empty Trash.
If you point to the Trash icon on the Dock and hold down the left mouse button (or the trackpad button on a laptop Macintosh) for a few seconds, a pop-up menu appears that's the same as if you right-clicked the Trash icon.