This screencast reviews how to manipulate passive and active voice.
Source: Kathryn Reilly
The following websites provide additional resources on changing passive voice into active voice:
http://www.towson.edu/ows/activepass.htm
http://owl.english.purdue.edu/owl/resource/539/01/
http://grammar.quickanddirtytips.com/active-voice-versus-passive-voice.aspx
Source: see above