I have moved the folder my photographs are in to another internal hard drive on my computer. I want to let Lightroom know their new locaton.
I am not moving the catalog just the pictures the little thumbnails in LIght room are linked to. I cannot find in the preferences anywhere to reset the path to the pictures?
How and where do I tell Lightroom the pictures have been moved?

You will have to import them. Go to the Library module, click Import and navigate to the where they are located. Select the photos you want imported and click Open. In the next window that opens, choose your import settings then click Import.