Hi and welcome to the site.
The information you seek can be found here mate:-
and dahmage is correct - you should own the blu ray or Digital Download releases to have the DeSpecialized Editions:-
‘Remember, as with any fan edit, YOU MAY ONLY DOWNLOAD THIS PROJECT IF YOU ARE A LEGAL OWNER OF THE OFFICIAL SOURCE. For Harmy’s DE project, this means YOU MUST OWN AN OFFICIAL HD RELEASE for each respective film (i.e. Star Wars Episodes IV, V, & VI), such as the official Blu-ray Disks or digital purchase.’
^ taken from The Ultimate Introductory Guide (which can also be found in the link above)