Only admins can delete project contacts from the system. To remove a user from your account, go to My Contacts and click on the users name to highlight the row. Then use the sidebar on the right to either delete the contacts Project Card or Personal Card. When deleting their project card, you will be prompted with a confirmation screen that allows you to delete the user from your My Contacts and replace everything they've added to the system with another user. When contacts are permanently removed they will no longer have access to your system and must re-register to gain access.
Removing contacts from projects
Only project managers and admins can remove contacts from a project. You may also remove a contact from a project from My Contacts or from the projects Overview section. From My Contacts, click on the users name to highlight the row and you'll see a list of projects they're associated with in the right sidebar. Once you hover over the project name, you'll get an x to the right of the project name. Simply click the x to remove them from the project.
You can also remove them from the Overview section. Once you enter a project, go to the Overview section and click on the People tab on the right. From here, hover over the users icon and click the x to remove them from the project.