How to add and remove users from a site
Introduction
This article will provide steps on how to add and remove users on a SharePoint Online site. You must have Full Control permissions or higher to do this.
Method 1: If using default groups and permissions
From the Gear icon in the top right corner, select Site Permissions.
From the pop-up window, select 'Share site'
Enter the user's email address and assign them a permission level (Read, Edit or Full control).
Once you "Share", this will send them an invitation and put them in the proper Group (Owners, Members or Visitors)
If you do not see the option to share, then you have custom permissions and must use method 2.
Method 2: Adding users to custom groups
1. In your site, select the gear, click Site information
2. At the bottom of the "Edit site information" bar, click View all Site settings
3. Under Users and Permissions, click People and groups.
4. On the left, select the group to which you'd like to add the users.
5. Click the drop-down arrow next to New, and then select Add Users.
6. In the box "Enter names, email addresses or 'Everyone'", type the name, username, or email address of the user and select them from the search box that appears.Include a personal message if desired, and click Show Options to choose whether to send an email invitation.
Instructions to delete users from a SharePoint site
1. In your site, select the gear, then click site information.
Under Users and Permissions, click People and groups.
4. On the left, select the group to which you'd like to remove the users.
5. Use the checkboxes to select the users you want to delete. Click Actions, and then select Remove Users from Group.
Click OK to confirm the deletion.
To quickly remove a user from all groups or locations in a site collection without doing it one by one, follow the instructions in KB0012217.