There are several ways you can delete people from your account. Once you delete someone from your account, any comments they've left or activity they've undertaken will be attributed to "Deleted user". They'll be unassigned from any Items they're assigned to, but all the content they've written will remain in your account.
Here's how you can delete them individually:
1. Go to People & Groups
2. Select the person
Choose the group and select the person you'd like to delete
3. Delete this person
Click the Delete this person link.
Here's how you can delete multiple users in a group:
1. Select the group
2. Select everyone
Click the cog icon and choose the 'select everyone' option. You can aso select multiple people (as opposed to everyone) in a group by holding down ctrl (PC) or cmd (Mac).
3. Delete Users
Select option to delete users.
Tip: Users are not notified when they are deleted from your account.