SQL Server stores history of all the taken backup forever. History of all the backup is stored in msdb database. Many times older history is no more required. Following Stored Procedure can be executed with parameter which takes days of history to keep. In following example 30 is passed to keep history of month.
DECLARE @DaysToKeepHistory DATETIME
SET @DaysToKeepHistory = CONVERT(VARCHAR(10), DATEADD(dd, -30, GETDATE()), 101)
EXEC sp_delete_backuphistory @DaysToKeepHistory
Reference: Pinal Dave (http://www.SQLAuthority.com)