As you may already know, Windows 10 Insider Preview builds have a pre-defined expiration date, also known as "timebomb". Microsoft limits the period of time the user can use a pre-release build of the OS in order to ensure that Insiders stay up to date with the latest features and updates.
If you are testing an evaluation version of Windows 10 and decided to upgrade to the full version, you will face a stumbling block. The evaluation version offered is of the Enterprise edition but Microsoft does not support any way to convert the evaluation version to a fully licensed version of enterprise edition! You cannot change the edition with DISM commands or using any other method. Even if you download the ISO image of the enterprise edition of Windows 10 and try to upgrade the existing "evaluation" OS, it will not allow you to proceed.
Here is a workaround which lets you upgrade Windows 10 Evaluation to the Full version easily.