In Baldur’s Gate 3, you will travel with a diverse crowd of characters, each with unique classes, talents, and personalities. These unique characters all bring something useful to your adventure, but you can only have four party members in your group. You cannot have anymore. There’s no party selection screen, either.
Each time you want to switch out any of your party members, you have to set up camp and have everyone prepare to take a long rest. A long rest is an excellent way for your characters to earn their health back and regain their spell slots if they’ve used all of their daily spells. While at camp, you can speak to all of the characters accompanying you on your journey.
Walk to the party member you want to dismiss from your party and ask them to stay in camp. They’ll act a little offended, but they’ll accept it. Once you have dismissed that party member, approach the one you want to add and ask them to join your party.
It’s a bit more tedious than having a party selection screen, but that’s how you exchange members. You want to make sure you choose wisely because wasting a long rest to change party members in and out may cost you, especially if you have limited opportunities to create a camp.