Upgrading from iCloud documents to iCloud drive I have lots of files stored in iCloud documents at the moment, if I upgrade to iCloud drive, are those files automatically copied across to iCloud drive, or will i lose those documents if i upgrade?
Those files should be copied across to iCloud drive with one caveat, you will no longer be able to access them with any devices using the old iCloud system. It is a one way update.

Here is a FAQ from Apple with more info.

http://support.apple.com/en-us/HT201104