This one catches out a lot of people. "The Content folder" in the top level of a downloaded zip installer does not mean you must have "a folder that must be named Content", it's "the folder set up in your Content Directory Manager dialog that contains your content files".

In early versions of DAZ|Studio this was actually named "Content", and that seems to have stuck for installers from many non-DAZ sources. Yes, that's horribly accident-prone. No, I don't think anything can be done about it at this late date.

Extract the folders from inside the Content folder in the zip and merge them into the existing folders inside whatever your existing content location folder is named.