Definition of level up in US English:

level up

phrasal verb

Gaming
  • 1(especially in a role-playing game) progress to the next level.

    ‘you can collect runes and use them as you level up to increase the power of your weapons’
    1. 1.1level something up (in a role-playing game) advance one's character to the next level of development.
      ‘build your army, level up your hero, purchase equipment, and challenge your friends to massive battles’