Hi,
We would be happy to have a look at the issue.
First, please make sure that you're up to date. We actually fixed a bug in recent versions of HikaShop which prevented the upload of big files in some cases.
Second, if you're up to date and it doesn't work, please provide the necessary instructions and links so that we can reproduce the issue on your website in order to check what's going on.
If you want to provide private information, please send a message through a contact form and include a link to this thread:
www.hikashop.com/support/contact-us.html