Here are some general considerations to take into account when upgrading from one release to the next.
- See the instructions in the UPGRADE.txt file of the Drupal download and in the upgrade section of the handbook.
- Read the Best Practices on test sites and don't do it first on your live site.
- Make sure that all the contrib modules you are using have an upgrade path or you are willing to upgrade them yourself or abandon them.
- Make sure you read and follow any instructions regarding upgrading any permissions modules you are using. Many have specific steps you need to take before starting your upgrade.