Roll back Articulate Studio 13 to Version 9?

Hi, I was wondering if anyone would be kind enough to help?

We recently obtained licenses for Articulate Studio 13 and installed the product on 2 end users computers, however they now want to roll back to Studio Version 9 so they can continue to use the custom skin (what ever that means). Unfortunately I'm unable to locate Version 9 in our software library. Any help would be very much appreciated.