You can select bunch of pictures in your catalog and press delete key > choose remove to remove them from the catalog.
If you want to start fresh and import folder by folder as you wanted to then, you can either select all and remove them all or create a new blank catalog and then, start the import process.
If you are willing to create a new catalog, go to File menu > Create Catalog > give it a name > choose the location where you want to save it.
This would open a blank catalog and then, you can start your import process.
Refer this tutorial : How to transfer photos from a hard drive folder to Photoshop Lightroom
Later on, you can get rid of the older catalog.
Thank you Chetna. I read the link you told me about. I also watched some youtube tutorials by Ben Willmore. He has a wonderful teaching persona, and is thorough, and takes into account the vast amount of variance in methods in Lightroom. He gives you an overview of each way, and then lets you decide. I've decided to import all my photos on computer to LR Catalog, using ADD function and leaving them on my desktop for now, and selecting minimal previews (since I never need full size and can always click on the thumbnail and wait while it loads.) I understand that I can then use Folders to create directories and organize my pictures inside lightroom, and by doing it this way, it leaves the same organized photo folders on the hard drive, at which time, I'll delete the ones I have all messy in crude folder form on my desktop to have less copies. I'm thinking the reason I had that many pictures in the first place is it's pulling from photos (mac lame photo software that they changed from iphoto last year) and maybe iphoto too, and then of course, my desktop copies. I was thinking I had around 36,000 or so; not three times that! YIKES! Thank you for your help!
Thank you Hal! I am going to try it with them, and then quickly disengage the subfolder option if it gets too confusing.