Please follow the below steps in order to remove a member to your Team/Channel:
1 - Go to the team name in the Teams list and click More options > Manage team.
For a Private Channel, click More options > Manage channel.
2 - Here you will see a list of all Owners, Members & Guests of the Team/Channel. To remove a member/guest, Click on the 'X' symbol next to their name. This will NOT prompt a pop-up screen and remove the member/guest immediately.
Only owners have access to do this
3 - The people you remove from a Team/Channel will no longer have access to the content in said Team/Channel.