This short guide explains some hints about upgrade the troops.
Guide to Upgrade Troops
You need to have the troop already in your formation and you need a Memory Star 5.
Keep in mind though, it only upgrades an individual troop, not the troops generally.
So if you have 10 knights in your team and you upgrade 1 you’ll have 9 knights and 1 knight+1 for example.
So it is pretty costly especially with how rare the Memory Star 5’s are.
Note: Also, you need to not have a full roster for whatever reason. So store one of your troops in the barracks.
Remember! If that +1 knight dies, you lose that +1 forever and have to upgrade another one. Just farm invitation letter through blue crystal and you can have as many 5* memory as possible idk if thats the most effecient way.