This wouldn’t have anything to do with the theme or how you’ve installed it. This just means that you haven’t setup WordPress correctly and that you cannot upload media in general. The reason is because your uploads directory is not writeable.
Basically, you just need to do what the message says. On your server, this directory needs to be writeable with permissions 755, 777, or similar.
And if your uploads folder already contains directories within (for example if this is a site that you moved from another server), you need to apply the permission changes recursively throughout everything in the directory. You should contact whoever has setup WordPress on your server.