If you'd like to add or remove users which will be able to manage your data (Contacts, Projects, Purchase Orders, etc.) you can do so by going into settings menu and selecting "Users" section. Invited users will not be able to change your company information or delete you as an owner. They'll only have an access to your contacts, projects, purchase orders and bills. It's your sole responsibility to ensure that you give access to a person you trust to manage this information.
You can find settings menu at the top right corner of the portal:
You should be able to see "Users" section there:
From this section you can view your current users that have access to your Appcrual portal.
You can invite new users by pressing "Invite" button and specifying their email and name. Invite email will be sent and they'll be able to join your company's Appcrual portal by following instructions in that email.
After an invite has been sent - you can revoke it if you've changed your mind before the user has signed up. All invites are located in "Pending invitations" section
Once the user has signed up - you'll be able to see them under "Users sections" and delete them if you wish to do so.