Theme problem

Hello:

I am having a really tough time getting themes to work. I uploaded a new theme and now I can’t get into the wp-admin dashboard at all. I went into filezilla to change the theme name to add “-old” as other threads in the forum suggest, but I can’t find the new theme in the wp-content/themes directory. Is there a way to change the theme back to twentyeleven so I can begin to fix this?

Thanks so much…