Instructions
Start a match that allows for character switching. These matches include "Duel," "Ultimate Training," and "Ultimate World Tour."
Select your primary fighter from the massive list of available characters, as well as that of your opponent, with a press of the "X" button.
Note the character portrait in the bottom right-hand corner of the screen. This portrait represents the character "in queue," or the character that will replace your on-screen fighter when you activate the switch. You can change the character in queue by flicking the right analog stick left or right.
Build up the purple bar below the character portrait by attacking your opponent and by blocking attacks. You cannot switch characters until the purple bar is completely full.
Press the "L3" and "R3" buttons at the same time once the purple bar is full to switch characters.
Refill the purple bar with attacks and successful blocks to switch to another character. You can switch characters as many times as you like during the match, as long as the purple bar is filled each time.