"Grand Theft Auto 5" character changes are done by holding down on the directional pad and selecting the single-player mode characters of Trevor, Franklin or Michael by using the right analog stick to highlight the desired character. Selecting your "GTA: Online" character automatically launches the online portion of the game.
Some missions in "Grand Theft Auto 5" require the player to switch characters in the middle of the mission to achieve completion. The character select wheel on the interface flashes white on the portrait of the character that must be used at that point in the mission. When a character has been injured or is in danger of dying, the character portrait flashes red to indicate the need to take control of them.