For Android:

1. Select the hunting ground where the hunt will take place
2. Click on hunts under the map in the app
3. Select Manage on the desired hunt
4. Click on Change in the upper right-hand corner and click on the rubbish bin next to the person you want to remove
5. Save

For iPhone: 
1. Select the hunting ground where the hunt will take place
2. Click on hunts under the map in the app
3. Select Manage on the desired hunt
4. Click on the red symbol in front of the desired name and Clear
5. Click on Done