Am using LR5, due to volume and size of pics I use an external harddrive. LR references only the Local Drive C not the external one. Where do I change that for LR to read the external drive. Appreciate help.
You need to right click/ command click on each folder and choose Update folder location and choose the location for that folder on the external hard drive to update.
If you have removed the images from your local drive, then you need to relocate the missing files.
Refer this link to relocate : How to find missing photos in Photoshop Lightroom
LR is not a file browser. It only knows about drives that you have imported pictures from.
If you have previously imported these pictures, then later moved them to the external drive, go to the Library Folders panel and "update location" on the folders that you moved.
If you have never imported these images on the external drive, do an import using the "add" option (not "copy") so that the images stay on the external drive during the import.