installing new themes on wordpress

hi there! i hope you can help me…i am new in wordpress..

i installed wordpress 2.7.1 on my server and everything is ok, now i uploaded the theme autofocus to the server and it shows on themes link, but i can´t change the theme, on the instructions it says that i just have to do a click on the image theme and it will change…but i do it and nothing happens….

i can´t change either to the classic theme…so i dont know what to do… plz help!