\usetheme{Darmstadt}
\usetheme{Singapore}
\usetheme{Szeged}
\usetheme{Copenhagen}
\usetheme{Luebeck}
\usetheme{Malmoe}
\usetheme{Dresden}
\usetheme{Ilmenau}
\usetheme{Berlin}
\usetheme{Hannover}
\usetheme{Marburg}
\usetheme{Goettingen}
\usetheme{PaloAlto}
\usetheme{Berkeley}
\usetheme{Montpellier}
\usetheme{JuanLesPins}
\usetheme{Antibes}
\usetheme{Rochester}
\usetheme{Pittsburg}
\usetheme{Warsaw}

- goes before \begin{document}
- one theme can be declared only