Upgrades are special skills or abilities that can be purchased for each individual hero once they pass certain level upgrade thresholds. In general, upgrades are available at levels 10, 25, 50, 75, and 100. At that point, you will have to pay additional gold to unlock the ability and have it count to your achievement. The type of upgrade (special ability, DPS multiplier, etc.) does not matter, just that it is purchased.
As you purchase upgrades, you will progress through the following in-game achievements, symbolized by a Heart located at the very bottom of the achievement list:
* Considerate (Purchase 25 upgrades)
* Generous (Purchase 50 upgrades)
The achievement will unlock once Generous is unlocked.
Tracking of progress in-game can be done two ways:
1) Selecting Generous (it'll show progress as # of upgrades and % to completion)
2) Going to the in-game stats page, which has an "Upgrades Purchased" counter (eleventh one down)
It is probably best to earn this one naturally, by progressing, leveling up your heroes, and buying the upgrades when you can afford them. Xbox achievement tracking does not update during the game, which makes it extremely likely that unlock requirements are tied to the in-game achievements being unlocked. As such, uninstalling and reinstalling will not allow you to quickly earn this. At this time, ascensions do not reset progress towards this achievement, but as there are around 90+ skills to purchase prior to upgrading "ASCENSION", you should be able to earn this achievement beforehand.