You can acquire skill slots as you upgrade your Characters

 You can get up to three skill slots and it can be chosen from the 'Skills button' located on your Friends Selection screen.

Skills can be acquired or replaced with Skills Tickets or Rubies. The Skills vary from Characters so keep in mind to check the 'Skill List' on the right side of the Skill Screen.

In addition, one character cannot have more than two same skills, so please take note of this as well.

* Photos to help you understand may differ from the actual game screen.