In the Library module with photos
selected in the Grid view, or with a selected photo in Loupe, Compare,
or Survey view, choose Library > Rename Photos.
In the Rename Photos dialog box, choose an option from
the File Naming menu. Choose Edit if you want to specify a naming
option using the Filename Template Editor. See The Filename Template Editor and Text Template Editor.
If you specify “sequence” for a naming option, Lightroom
numbers the photos sequentially. If you don’t want the numbering
to begin with “1,” type a starting number in the Start Number text box.
