How do I change Software Update server to official one on OS X Lion (or later)?

Solution 1:

It depends on exactly how they changed the update server setting. If they did the obvious thing, this should delete the setting (so it'll go back to normal):

sudo defaults delete /Library/Preferences/com.apple.SoftwareUpdate CatalogURL

If that doesn't work, it's possible it's configured as a per-user (rather than system-wide) setting, in which case this should do it:

defaults delete com.apple.SoftwareUpdate CatalogURL

Solution 2:

On system newer than 10.10

sudo softwareupdate --clear-catalog

Solution 3:

Before driving to the Apple technician, you can type the following Terminal command:

defaults read /Library/Preferences/com.apple.SoftwareUpdate CatalogURL

This will tell the the URL that SoftwareUpdate is checking.