Replace BAK file on each backup job

Hi,

The thing is that my command doesn´t replace the file and it adds the backup to the previous one, so it grows and grows in the time. Any ideas?

thanks!

BACKUP DATABASE [mydb] TO  DISK = N'C:\Users\Administrador.Documents\Visual Studio 2010\Projects\BAKs BBDD\mybackup.bak' WITH NOFORMAT, NOINIT,  NAME = N'my_backup', SKIP, REWIND, NOUNLOAD,  STATS = 10