The question of how to Delete a Project, comes up with some regularity. People will complete several Projects, and realize that a lot of disc real estate is taken up by the files involved in the Project, and they will want to free up that space for new Projects.
The answer is simple, but the actual operation of Deleting everything associated with a Project, might require some Searching, and work. It all depends on how one set the Project up, to begin with. One highly recommended structure is outlined here: http://forums.adobe.com/message/3998053#3998053
Such a folder structure makes Deletion of a Project very easy - in, say Windows Explorer, just navigate to where that Project's main folder is located, and Delete it. All of the sub-folders, and files will be Deleted, as well.
If one have Projects scattered about, and they have not created a concise sub-folder structure, or they have Imported Assets from all over their sytem, things become a bit more difficult. One has to match Project names, with several Scratch Disk folders, such as the Media Cache, AutoSaves, and the like, then they have to find where there Assets are. Warning here: I only work with Copies of my Assets, so the originals are safely stored on my NAS. When I Delete a Project, I am only Deleting the Copies of those Assets. Consider Deleting original Assets, before you do it.
Also, one should take something else into consideration - "Will I ever wish to revisit this Project again?" If the answer is absolutely not, then Delete away. If there is even a "maybe," consider using the Project Archiver function, to make a copy of the Project, with Assets, and store that on an archive drive.
Remember, the PREL, the Project File, does not have any of your media, but only links to where that media was stored, when Imported. See this article for more background: http://forums.adobe.com/message/3392837#3392837