How do I remove someone from my team?

まだ日本語では提供されていないため、原文で表示しています。上のメニューから翻訳できます。

Only the captain can, and only before registration closes. Open your team in the registration panel and remove the member there; removing them cancels their registration for that tournament.

A captain cannot remove themselves — use Withdraw for that, which hands captaincy to a remaining member.