Hello PROBERT1968,
If you replace the original images (under the same filenames), there's no need to use Change Path option to fix the paths. To update the thumbnails, remove them by right-clicking on the chunk's label and choosing Remove -> Remove Thumbnails option.
To modify the image brightness via Adjust Levels command you should select the images, that require such correction, in the Photos pane, choose Adjust Levels command from the context menu, then modify value in "Average" field, where the value means the % from original.