How long messages will be stored in the topic / section using kafka 0.9

Question

I use kafkaConsumer api to retrieve data from the topic (one section for each topic), after all the records have been obtained by polling and processed, if a new instance of kafkaConsumer is created and try to extract data from the same topic / partition, then I can get same data as the first time. Is there a way to delete entries from a section / section after it has been used?