You can't upgrade limited units. You can only unlock them, and each subsequent level.
Before the fragments that ment you had to end up in ucl (top 2%) on Tatooine 10 times, to get it to level 10. Ever since we got objectives and reward crates, you could be so lucky to get it as a reward (but i only got it ones during a whole year)
Now with the fragments you need to collect 32 fragments to unlock and level up your limited units. Which no longer requires a top 2% win, although it helps to get there faster.
Leader of Ruffnecks010 - Level 44 Imperial squad - ~2650 on Leaderboard
Rank 1010 on SoD. W:70 D:1 L:18 | HQ10 - Rank 8 - 15k+ medals - 900+ reputation
We have room for more Squad War players