WP Opulous theme

OK this is what has happened and I cannot get round the problem.
I had built my video site on free WP Opulous theme a couple of months ago and was getting on quite well getting more visitors and adding materials, then overnight the theme updated itself and put in the new version of WP opulous, which I do not like the layout of. I got in contact with Nimbus themes and was given a link to old versions of the theme. I have tried many older versions but the new one comes up every time I try and upload an older theme.
I cannot understand this. I did not want the theme to be updated in any way and can’t understand why I can’t upload an older theme, why is the new theme overriding older themes?
I don’t know any programming and was using wordpress to get my video site online. Why can’t I get the old theme up and running again?
Any help would be massively appreciated.
Mo