To upgrade automatically, use MandrivaUpdate.
Please verify the update prior to upgrading to ensure the integrity of the downloaded package. You can do this with the command :
rpm --checksig package.rpm
You can get the GPG public key of the Mandriva Security Team to verify the GPG signature of each RPM.
If you use MandrivaUpdate, the verification of md5 checksum and GPG signature is performed automatically for you.