Depending on the Raider you're facing, there are two ways of acquiring Ultimate D Change. This state has no passive Limit drain and heavily reduced Super cost.
Firstly, if Dragon Balls are scattered around the environment, you can collect all seven and take them to an altar to summon Shenron. After an interaction, you can choose "Give me more power!" to become Ultimate, as your level 3 character but increased to level 4.
As of writing, only matches with the Broly or Zamasu Raiders feature Super Transpheres. When certain conditions are met (normally the Raider is a certain level and there is no Ultimate currently active) and a short time has passed, a Super Transphere will spawn in a random spot on the map. Interacting with it will make you become Ultimate, however your character, Super, and level are specifically chosen by the developers.
Land the finishing blow on a Raider while in Ultimate D Change. It can be any kind of attack.