Do what the accountants do: close the old books and open new ones. Initialise relevant accounts with sums from the old books.
Edit: that said, I've found spreadsheets to be some of the most convenient ways to do high-level double entry. Just so you don't assume you need to learn a new tool to do it.
Edit: that said, I've found spreadsheets to be some of the most convenient ways to do high-level double entry. Just so you don't assume you need to learn a new tool to do it.