Much better:
ALTER TABLE records MODIFY id INT UNSIGNED AUTO_INCREMENT NOT NULL;

The real key there is the “unsigned” – it gives you twice as much storage in the same amount of space. And the query runs nearly simultaneously, as opposed to the hour+ it takes to change the size of a field in a table that long.

Another observation: why are all of the fields in the records table nullable? Best practice is usually to make them non-nullable unless for some reason nulls are really needed (and they’re usually no).

JFWIW.