Currently we do not support a way to directly remove someone from your Pool, however this is a feature on our short-term roadmap.
In the near term, you are welcome to start a new Pool and not add them, which should accomplish the same thing. Funds from the old Pool can easily be transferred into the new Pool.
In addition, the member you wish to remove can be transitioned to a Viewer. Viewers cannot spend, add, or invite members to the Pool. This change can be made by the Admin or Owner.