Audit failed/successful login LOG

Hello everyone (:

I have some Audit issue on SQL Server 2008R2 version, standard edition.

I want to Audit failed and successful login, so to do that i'm right click on the instance --> Properties -> Security, and choose the option "Both failed and successful logins", and save.

The only problem is that he keep a lot of successful events, and I just want to save the last month and that's it.

How do i do it ?