By this feature we can use DBMS_STATS.RESTORE... procedures.
The default retention for Optimizer Statistics History is 31 days. Old information are automaticly deleted by Oracle Database. Without any manual intervention.
But sometimes this 31 day retention may be too much. In one of my database this component was 75 GB.
--Check SYSAUX components and their sizes.
select * from v$sysaux_occupants order by space_usage_kbytes desc;