There’s no stopping change.
And there’s no stopping the reaction of a tech client who might be less than enthralled with whatever necessary changes you had to incorporate to save their data, upgrade their Mac and/or get their Mac working again. Yes, their computer is back, but something is either slightly or radically different and this is sticking in their craw. A user interface has changed in the new version of Microsoft Office, they liked the old version of iTunes better, or they didn’t expect those new icons in that new version of Mac OS X that you had to install to make a print driver or application work.
As much as this may add to your workload (it’s generally implied that you’ll spend some time off the clock explaining the new changes they’re seeing), their frustrations are not unfounded. They had something that behaved a certain way, they’d become accustomed to it, and now change has been thrust upon them without their input. Add in the fact that hardware, software, and your time as a tech aren’t cheap and potential frustrations with the upgrade can become that much worse.

Perhaps the first thing for any tech to understand is that while you’re obligated to help explain the changes caused by an upgrade and how they might be necessary, this is not an invitation for indentured servitude, complete with the client calling, emailing or demanding the tech come over pro bono and explain the changes created by the upgrade yet again. That being said, there will be nightmare clients who ask for more than can be reasonably given. This is why referrals were invented, even if they’re just a more polite way of telling them to take a long walk off a short pier and voice their grievances to the local sea life.
What can be done, and the best way to find a balance, is to take the following steps throughout the process.
Explain the need for the upgrade and why it’s necessary.
Walk them through the upgrade as you’re implementing it.
If there are different steps that need to be taken by the user once the upgrade is complete, write them down, go over the steps with them again and print out copies of the documentation for both yourself and your client.
YouTube is your friend and its instructional videos are not to be denied. If your client is worried about how to learn to use a new application, piece of hardware or version of an operating system, odds are you can point them towards an instructional YouTube video, bookmark the video for easy access later and perhaps save the link to the desktop as well. The person in the video teaching the viewer how to perform a process is probably feeling more patient than you are and can be accessed at any time. Take advantage of this.
Finally, set the parameters. Yes, you can explain the new changes that follow an upgrade pro bono, but you’ll need to define your limits, whatever they may be. Explain things as best you can, provide them with instructional video links and helpful FAQ bookmarks before leaving, distinctly state when you’re charging, when you’re on or off the clock and what times are or are not appropriate to call with a tech question. If both sides know what to expect, the tech/client relationship can grow and last through the years.