Upgrading the system is closely related to initial rollout, but it has the additional twist of being able to roll back to previous versions, minimizing system outages, minimizing user downtime, and so on. While it may be acceptable for an initial rollout to employ an installation wizard such as Wise or Installshield, for upgrades such tools are less than ideal. They typically require the user to click buttons, enter details, and even offer the facility to specify paths, among other things. This is fine for software intended to be used by an individual, but in a corporate environment, control of the desktop is very important for cost-effective maintenance. If at all possible, make upgrades zero-touch. It may be possible to drive your preferred install tool from a configuration file; if so, do so.
As for rollout, be sure that you know how to roll back a release that proves faulty. If database changes have been made, this can be particularly tricky. If you use an automated delivery tool, make sure that it can backtrack what it has done and report failures so that you know what went wrong and why.