Secuirty Best Practices (How I upgrade?)

[ergos]

Hi all,
I am new to Plesk and I am a bit confused.

Which is the best way to deal with security issues?

I have closed services that I don't use (via plesk), I have configured the firewall module of plesk but still I don't know how to deal with bugged program already installed.

How works the upgrading in plesk? I must wait for a new release or i have to patch manually?

And if I patch manually after Plesk works or there will be problem?

In particular if I want to upgrade Apache and Php I can do it via yum (I have cent os) or there are any problems I should consider before?

I am using Plesk 8.0.1 and CentOS 4.3

Thanks in advance,
Filippo