To edit the channel information and the channel members of a certain channel, first select the specific channel and open the channel information by clicking on the channel name at the top.

By clicking on the button "Members" the member overview will be displayed. There you can edit members with the three dots menu. The following options are available: "Make channel admin" or "Downgrade to member" and "Remove from channel".
You can also add new members by clicking the "+" Button in the upper left corner. These can be found faster with the search function. After that, add them to the group with the "Add" button.

In the channel information, there is also the possibility to mute the specific channel to prevent receiving push notifications. This is only possible for yourself and not for others.