if this happened during the process of the upgrade, and you chose to "reserve nothing" when upgrading, your data might has been overwritten. If not, you may be able to recover some of them. Anyway, just use some data recovery tools to see of they can get anything. Recuva as mentioned above is a good one, Easeus data recovery or 7 data recovery. Easeus data recovery can deep scan the partitions or hard drive.