Upgrading from 2.2.1 to 2.7.1

I need to upgrade WordPress 2.2.1 to 2.7.1 but have read on various sites that this may be a big jump and might break the site. I’ve noticed in the latest version there are more security checks such as unique phrases. Do I need to do the upgrade in parts or is it possible to do it in one go?

Any advice would be much appreciated.