PokerTracker

How can i delete handhistorys, that older than 6 mounts? Or how can i delete handhistorys and keep tha latest 3.000?
Thanks!

Use the Advanced Purge button on the Utilities > Database Maintenance and Options window where you can tell it do delete hands between 2 dates so you can enter the ranges you want to delete.

And how can i keep out myself? This option is "Observed Hands Only"?

Yes, the Observed Only option will only delete the hands from tables you were observing and not playing at.