Unforuntately there is no direct upgrade path from 2014 to 2016. User's upgrade from 2014 to 2016 will fail due to database compatibility issue.
Line 2286: Error: The upgrading path is not supported from version 4 to version 10. Please contact our support team.
2017-04-07 16:27:22:172  ERROR com.erdas.iws.config - Current database version(4) does not match the current Apollo Essentials release which requires database version(10).
2017-04-07 16:27:22:173  ERROR com.erdas.iws.config - Unable to copy database file (QSQLITE) to the backup file (QSQLITE.backup) and a new database is created. Please upgrade the existing database backup if needed.
There are two options:  Install Apollo essential 2016 from scratch, delete the filelist.db, and then generate all services manually again in Apollo essential 2016.
 Upgrade Apollo essential in incremental level. Each of the database upgrader can upgrade from the previous version without issues, so if you install each new version of APOLLO Core/Essentials, and perform the upgrade, it should work. In order to upgrade from 2014.0 to latest 2016.2, you have to follow the following order:
1. 2014.0/2014.1 -> 2015.5 2. 2015.5 -> 2016.2
Basically for users upgrading from v2014.x, they need to update to the v2015.x version first, then from there upgrade to the a later version. To upgrade to the latest version, the above workflow is recommended, Version 2015.5 should be the intermediate version.
Or user can always follow the complete upgrade path:
When installing, you also need to go through the entire installation processing, install the files and run the configuration wizard. The upgrade of the dataset happens during configuration wizard stage. When uninstalling, keep the configuration.
Unfortunately this workflow is not documented in the Apollo essential 2016 user guide. Here are the installers: