@Viktoria Michaelis -
This rather defeats the object of the game. It means that I need to download a theme and then upload it to my server before I can see whether it is one that I like, one that fits in with my project. How many thousand themes are there on WordPress.org? If I just cut it down to simple things like 2 column, blue… still a lot.

Wait: are you actually manually downloading Themes from the Theme directory?

If so: why? Just go to your Dashboard, then Appearance -> Themes -> Add New, and you can do it all in one click. No need to leave your WP-Admin. :)