If the limit of invitations to a Clan is reached, no more members can be invited. It's also impossible to send more invitations than the limit allows (even if some of the sent invitations were not accepted). That's why before inviting a player to Clan it's better to contact him, learn his priorities, the time he can spend playing, etc., and, correspondingly, send an invite when it's for sure the player will accept it.

In order to leave a Clan:
Enter the Diplomatic Corps, choose the "Clans" tab and click "Leave the Clan" button next to the Clan name.
You won't exit the clan immediately, but in 1 day, after the countdown. The exit can't be cancelled.
The Clan Head is able to construct Clan Warehouse and Clan Reservation buildings.

Clan Heads, be careful, don't confuse buttons. You also have button - "Disband Clan".

Player Expel from clan.
The Clan Head can expel a player from the clan. In order to do that, click the player's name in the "Clans" tab of the Diplomatic Corps and click the button "Expel player from Clan" in the pop-up panel. The player won't be expelled from the clan immediately, but in 1 day, after the countdown.

Clan disbandment.
The Clan Head can disband the clan. The disbandment of a registered clan will be done in 1 hour, after the countdown. During this time the disbandment can be cancelled.