First, not every Nexomon evolves, but all the ones that do will only evolve via leveling. There are no special stones or anything that you'll need (like you would in Pokémon). The lowest level at which a Nexomon evolves is 11, and the highest is 50.

What level do Nexomon starters evolve?

Finally at level 32, it's going to evolve into Kitsunox, the warrior Nexomon.

What level does ACCA evolve in Nexomon?

Acca is an Electric-type Nexomon that evolves from Velokitti at level 14. Acca evolves into Jeeta at level 36.