Application Upgrade

Hi!
Everyone morning my rkhunter installed on my debian lenny generates report and its displaying me warning that my applications gpg, openssl,sshd is out of date, and possibly a security risk.
I have openSSH_5.1p1 version, Openssl 0.9.8g version and gpg 1.4.9 version.
The question is how to upgrade these apps and if i upgrade it on my running servers will the upgrades affect any other apps functionality.
Thanks