Ok....
So new to linux.

Finally got this here thing up and running, using redhat 7.1 right now.

SO my question is, if I wanted to update to RH9 for maybe even slackware or something.....
How would I go about doing that?
Do I just install it like I did this distro (meaning just have the boot CD and letting it run) or is there some kind of linux thing that will let you update the OS?

Can but you cannot change the distro. Should be the same distro as the old one.
Most user friendly distros like redhat, mandrake, suse have update features like windows. When you install it, you will be asked whether you want to upgrade the existing system or clean install. I don't know about slackware. Since slackware doesn't have package manager, I don't think it can be upgraded. Not sure.

When you upgrade, make sure backup all your important data. Upgrading is not always successful. I failed my upgrading from Redhat 8 to 9 so I ended up clean installing.

Slackware has a package manager, it's called pkgtool.