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I assume that you want to migrate the content (pages and paragraphs) and not generate files (old templates to layout templates).

There is no simple tool that does this, AFAIK.

You can either use Data Integration (export as XML, Import with XSLT transformation) or do some SQL magic :)

I once did this by SQL on a site, which was using a lot of paragraph setups and columns. It was done on a copy of the site first ;-)

1. "Normalize" the pages as much as possible and reduce the number of different templates (SQL).
2. Create the layout templates.
3. Define some mapping rules - from current paragraph setup templates, columns and paragraph sort order to the new layouts and containers.
4. Write the SQL updates (or XSLT depending on the method you prefer).
5. Run the updates and pray.
6. If everything worked as expected, do the same on production site (backup first).

This is not bulletproof and you will probably have to do some manual work afterwards.

You could create a copy everything to a new area / website before you start, so that you keep the old website and work on the copy until it is done, then make the switch. Which approach is best depends on whether content on this site is frequently updated or not.