You generally do not need a new Lightroom catalog. The safest approach is to reorganize the folders from within Lightroom so the catalog always knows where the files are.

Use the Folders panel in the Library module to create the new year/month folders, then drag existing day folders or selected images into that structure. For example, create 2006/01 and drag 2006-01-07 into it, or move all images from that month into a single month folder if that’s your preferred layout.

The key point: do the moves inside Lightroom, not in Finder or Windows Explorer. If you move folders outside Lightroom, the catalog can lose track of the files and you’ll have to relink them.

There’s also no strong need to over-organize by date in the folder tree. Many photographers keep a simple year/month folder structure and rely on Lightroom’s metadata, search, and filtering tools to find images by exact day, lens, keyword, or other criteria.

So: keep your current catalog, create the new folders in Lightroom, and drag/drop the existing folders or photos there.