If I've just sent you a link to this page, it's because I realized I didn't explain how I usually do Drupal updates. Apologies for that and hopefully all of this is old hat to you. For anyone else who's stumbled across this page, here's a relatively high level overview on how to safely update your Drupal site within a major release (e.g. 6.18 to 6.19).
Step 01: Make a Backup of Production
Everything you ever do with a Drupal site should start here.