We kept the upgrade path open for 1.0 for a full year. It was removed roughly a week ago.
Please note that 1.0 is *enormously* out of date. Since then we have had 1.1, 1.2, 1.2.1, and right now as of today, switched to rolling release, 2017.01.01.0.
As your system wasn't upgraded for over a year, it is completely insecure. I would highly advise reinstalling with the latest ISO, either Budgie, or MATE, of your choosing.
https://solus-project.com/2017/01/01/so ... 0170101-0/
Installing the Budgie ISO will give you the most updated and complete experience.