Alliance Captin cannot be changed, except in the following cases:
1-If the alliance leader steps down and hands over leadership to another member, this can be done through the following steps:
-Click on the alliance icon at the bottom right of the screen.
-Select "Members."
-Click on the desired member.
-Choose "replace captain."
2-If the alliance captain has been offline for seven days, R3 or R4 members can spend 1,000 gold coins to replace them!
You can do so by the following:
-Click the alliance icon on the bottom right of the screen.
-Click on members.
-Click on the captain and choose "Replace Captain".