It's simple to remove a member from your group.
1. Course View
Go to your Course by tapping the book icon.
2. Group Details & Remove Members
Tap the name of your group at the top of the screen. This will load Group Details. You'll see the headings Members, Details, Course and Notes. Under Members, you will see a list of everyone in your group with an 'X' beside their name. Tap the 'X' to delete the member from your group.