No, I suggest you leave Photoshop CS5 installed, unless you really, really need the disk space.
It can come in handy if you want to see how something used to work.
As Noel suggested it is best to leave old dogs lie.
However, if you have it in your mind you don't want CS5 on a computer, it is best to deactivte and uninstall BEFORE you install CS6. Some users experience file association problems, and other problems, if they uninstall old version after installing new version.
Noel and Curt,
Thank you for your quick replies. It is not a matter of needing the disk space, but rather I want to "waterfall" my two working copies of CS5 onto two different machines, that now currently have CS4 on them.
I'll try Curt's procedure on my laptop first and see how that goes before I then perform the same operation to my "studio" workstation.
Shhhh. You're not supposed to do that. But if you're going to uninstall it's better done first.