You're talking about the 1. Blitzkrieg i think.
During the campaign you have most the time the primary mission(s) and 3 different secondary missions.

The easy and medium Missions offer several Upgrade-Options at once most the time but you can do only one Upgrade per MIssions done, just switch through the Unit-groups to see the available Upgrades.
The easy and medium Upgrades are at 90% Upgrades that are available for free and at infinite numbers
after you finished the current chapter/warzone.

The hard missions offer 1 Upgrade/victory too but only for one of the shown possibilitys and sometimes even the number of Upgrades for one of the possibilitys is limited. If i remember right...there is a row...like 1.Upgradeoption will be given at 1.,4.,7 victory, 2. Upgradeoption at 2.,5.,8. victory, etc. If one Option is no longer available, it will be removed from the mission-briefing.
At 90% the Upgrades of the hardmissions aren't vailable after finishing the chapter/warzone and you have at least finish the next chapter too to get a equal upgradeoption, sometimes they are the only chance at all to get Upgrade X.

All secondary Missions can be repeated infinite, as long as you don't finish the chapter/warzone.