Welcome to the forums! Please check out theme documentation if the backround changing process is already described there. In case of further questions you can contact theme author for support:
Thanks Luca for replying,
The documentation has no information about anything related to the theme. however, I did contact the theme author but no reply.
I’m in no way related to theme author, but it may take up to day or two to get a support response. Please wait a little longer, I’m sure that @ThemeLan will get back to you as soon as possible
If you don’t get response in a reasonable time, please read these articles to find out if and how you can get a refund:
I’m sorry it turned out that way. Be aware however that changes to theme that involve editing it beyond original features are not covered by item support:
If you won’t find a way to edit background and it was not advertised as theme feature originally, you may be interested in hiring a professional from Envato Studio that will make necessary changes for you.
If you feel your refund request should be accepted, you can contact Envato Help and Support for further explanations.
I purchased the theme Flanger from ThemeForest, however, I had a question about the bg I sent it to the theme author. The question was:
in which style sheet and what line I can find the bg, so that I can add a call for it.
After waiting, I sent a request for refund, so the author immediately replied with a decline, but he didn’t bother to answer my simple question to resolve the issue, which make the 6 months support to theme useless and misleading.