Update Drupal core from a low version
As long as core is not modified in any way, there should be no risks of updating it straight from 7.14 to 7.31. It will apply all database updates from each version in between. There's literally no difference in doing it one version at a time compared to doing it straight to 7.31.

But as always, test it in a development environment before doing it in production and always make backups.