Change all dup-references to references to MAX(id)

This is a question about sqlite.

I want to remove all duplicate entries from customers (keeping the MAX(id) entry). But before that, I want to change all references in orders to the corresponding MAX(id) value.

This is what I think does the right thing:

UPDATE orders
SET cid = (SELECT  MAX(c.id)
           FROM customers c
           JOIN (SELECT  name, id
                 FROM  customers
                 WHERE id = orders.cid) q
           ON c.name = q.name
           GROUP BY c.name);

DELETE FROM customers
WHERE id NOT IN (SELECT MAX(id)
                 FROM customers
                 GROUP BY name);

But especially the first command is extremely slow already with some 10,000 customers. Is there a faster way to do this?