You have two options really you can move LB to your other drive and then delete all of your platforms but do not delete any of the media you already downloaded it will still be there when you reimport you ROMs again you will just chose not to download any of the media from the LBGDB or Emumovies this will speed up the import exponentially. Your other option is to not delete anything and to use Notepad++ to edit the paths to your game from the old path to the new path. You will use the find and replace function found in the Search section of the menu bar. you will type in you old paths and then hit count to make sure it finds them in the xml and then you switch to the replace tab and type in the new path and hit the option to replace all. Save the xml. You have to have LB closed while you perform the editing so make sure it is closed before you attempt to do it with this method.
You will have to do it for every platform