I tried to upload a file this morning, and 8 hours later, the Design Studio is still displaying the wheel of death.
It certainly shouldn't be taking that long. There are a handful of variables that go into it, but a big one is the location of the file where it is being uploaded from and ensure there's a proper connection between the two. Otherwise, ensure the file itself is not corrupt, as well as keep the file size as low as it can be (compressed, etc.).
Could you possibly be over the 50MB file size limit? Also if you expand "File Details" you can see if there are other files in queue to upload first and you can cancel them.
Retrieving data ...