To edit your character lineup for battle, go to the Living World and select a sector of the city you wish to do battle in. Choose the Campaign node you prefer to bring up the battle screen. After tapping on the Battle (Energy) option you will be brought to the Team Select screen just before battle.
Tap the Edit Team button just below the portraits of your five characters to bring up the edit screen. Tap on an existing team member to remove them from the group and make room for a new one. Tap a new character from the field below and they will be placed in the empty slot you created.
You can also swipe right or left on the team of five to make a new team entirely. You’ll notice the words “Battle Team 1” on the first team, etc. forth as you swipe left. You can preset many teams at once using this method and choose the best one for your needs instead of editing the core five every time.
When you hit the Save Team button it will save that team for use. You can also use the “Recommended Formation” button with the Thumbs Up. This will automatically select the top five strongest heroes for the mission, but be careful it may not take into account all synergies, balanced powers and could leave a hero or villain open to a color vulnerability.