Open the catalog in the new location. You can do this by double clicking the *.lrcat file in Windows Explorer, or by holding down Ctrl while opening Lr. (This option should open a dialog allowing you to choose a catalog to open; navigate to the catalog in the new location.) Once the new catalog is open, everything will seem fine, but if the original photo file copies still remain in the original location, the catalog will retain its now outdated links to them. Right click on the highest level parent folder in Lr, and click 'Update Folder Location...', which provides a folder navigator for you to locate the images in their new location. This should fix all the photos and folders in the selected parent folder. If there are additional parent folders on the top tier, repeat the Locate... process.
Two caveats:
1) To avoid potential future confusion, be very careful that you've opened the new catalog copy. Once complete, you may want to temporarily rename the folder tree with the old images to verify that the new catalog has been pointed correctly to the new image location. Once you're sure all is well, delete the old images.
2) BACKUPS of the catalog lrcat file, and the original images are crucial. Once you've deleted the old images from the original drive, you're flying without a net. Personally, although I've never had a single problem with this process, I wouldn't try it without at least 3 copies of the catalog/images. a) the original catalog/images on the old drive, b) the new copies on the new drive and c) a complete set of backups of the catalog/images somewhere else.
Oops, I just noticed this is your first post here, Welcome to the Forums.....
