How to install Photoshop CS upgrade?

What version of CS are you talking about? There's CS through CS6. The installer  of the upgrade version you want to install will simply ask for a qualifying product serial numbet to continue with the install. If you are installing a full, but not upgrade version, no prior versions are necessary.

CS versions prior to CS4 can not be installed and activated with their original installers.  CS4 and newer upgrades should be able to be installed and activated  using the CS versions installer with your Upgrade serial and a your the product serial you are upgrading from. That version need not be installed. However, you need your serial for that version. Your two serial are required during activation.

A CS6 Upgrade requires a CS5 serial that you are upgrading from. CS5 Upgrade and below just require any older CS version serial.