Eso mismo hago, pero me aperece y no deja hacer nada más que esto...
elijo tema y no va, queda el que esta.
Easy Theme Installation
Enter the URL to the theme zip file and click Install theme.
Usage
Select a theme to preview live on the site. Only administrator will be able to see the selected theme.
Additionally you may add "?theme=xxx" to your blog url, where xxx is the theme name you want to test.
Theme Test Drive is Disabled.
Así,
http://www.prelovac.com/vladimir/wordpress-plugins/theme-test-driveYou can specify the level of users to have access to the selected theme preview. By default it is set to 10 (admin only). Level 7 are editors, level 4 are authors and level 1 are contributors. The access level is ignored for accessing the site with ?theme=xxx paramaeter.
Access level
Disabling: If you wish to stop using Theme Test Drive, press Disable button. Alternatively, disabling this plug-in should also do the trick.