You can remove a friend by following the steps below:

1. Tap the "Leaderboard" tab in the bottom navigation bar
2. Tap the "Friends" tab
3. Tap the "Friends List" tab
4. Tap a friend's player card you want to remove from your friends list
5. Tap the "Remove" button

Note: When you remove a friend from your friends list, you are also removed from that friend's friends list.