Upgrade process is very simple:
If you are using versions 3.0 to 3.2, you have to upgrade to version 3.3 first before upgrading to the latest release.
If you are using version 2.x, you would have to manually migrate database schema. See Update from 2.x to 3.0 for more details.
Above instructions are made with assumption that only configuration file is modified. If any other files (e.g. templates) are changed in the old version, you need to re-apply those changes in the new version as well. Note that old templates are not guaranteed to work with a new version.