There are various reasons why you may want to restrict access to your portal- the user left the company or is no longer on the partnerships team, etc. As a Partner Account Owner, you have the option to Suspend that user.
Log into your portal, and click on the Team Members tab. Find the respective team member and select the edit button next to their name.
In the pop-up window, you'll find the status drop-down that should be in the Active status. Click on the drop-down, select the Suspend status, and press save.
This team member is now suspended and an email was sent to inform them of this. They will no longer have access to the portal.
If you need to activate this account in the future, you'll follow these same steps and place them in an Active status.
For more information on Team Member's visibility, check out this article.