I have purchased Acrobat Pro XI through TechSoup and want ot install it on a different computer than originally installed, do I need to uninstall from the first PC before installing on the second PC?

you're allowed two concurrent installations and activations so you don't need to deactivate and uninstall.

however, if you're not going to use acrobat on your other computer, you may want to preserve that 2nd install/activation.

in any case, make sure you deactivate (help>deactivate or sign out) before uninstalling.