How to configure atop sampling interval & log path?

I installed atop version 1.26 on Ubuntu 12.04 server. By default, its sampling interval is 10 minutes. How can I change to 1 minute? Also, how can I set the log path? Currently the logs are at /var/log/, but I notice that atop added a folder /var/log/atop/ (empty). How can I set the logs to be saved in this folder?