problem ability learn

[DexterFstone]

Hi I make a hero and max leve of hero is 25. Hero has 4 ability (ablity 1 has 4 level and ability 2 3 and ability 4 has ult and 3 level) change level skip requirement ability 1 2 3 to 1 and ult to 5 and required level ult to 6 But you can't always learn a level of ability for examole ( 4/4/4/2)
How to fixed?