Help nonprofit migrate from Confluence 4.2.4 to 6.2

Our small non-profit organization, which provides digital libraries to over 1,600 schools in developing countries, needs help migrating from an older Confluence to the latest version. It's all tied to our migration from Drupal to WordPress. For years we've pulled occasional articles out of Confluence to include them on our Drupal Web site using XML-RPC. Now we need to get WordPress 4.7. and Confluence to play together with REST-API. From our brief research on the topic, to arrive at Confluence 6.2 from version 4.2.4 we may have to update to an intermediate version. The main plugins we use are Gliffy and Comala Workflows.