An Inquiry about Z visa extension

I am a Filipino (Philippines) who is holding a Z type which will expire on July 21, 2013. I have a sister who is holding the same one too and her own was just renewed on June 21,2013 which will expire on June 23,2014. Is it possible for me to extend mine from the city PSB where I am living now after my sister registered me to the local police station as a companion in her apartment?