If you'd like to set a pet free to make room for some new ones, take the steps below!
1. Open the pet menu by selecting the paw icon from your toolbar:
2. Any pets not currently on your Battle Team will be listed under Your Pets. Select the pet you'd like to release, then Info.
3. You can now release your pet by selecting Let pet go...
4. You'll need to confirm this by selecting Let go. You can cancel this process by selecting Keep.
That's it! You'll now have some free space to catch new pets!