unable to upload “structure” theme, says ‘unpacking package’

I have downloaded the free version of the ‘structure’ theme but every time I upload it, it appears to finish but then just says “unpacking package” but nothing is happening. It does not show up as one of my themes to activate. Any ideas as to? why and if I can fix it?

I have tried uploading the zip file to a folder but didnt know what to do next, like where to put it……