Hi,
Well the secret to this is usually the not-so-well-known fact that the various Microsoft rollback programs only work within 30 days of the point you ran the W10 upgrade. After, that the feature is disabled and won't work.
You don't mention what source Windows you upgraded from such as an earlier version of W10 such as v1607, v1511, v10240, etc. or whether you are going back to your original windows OS version such as W7 or W8x. In any case, it still applies, and the rollback won't work. You'll need to backup all your personal data to external media, and do a Windows reinstallation from factory Recovery media (DVD or USB or HDD partition), reinstall all your Programs from scratch and restore/reintegrate your data...