As owner, or user with full control permissions, you can add, edit or delete users for your SharePoint site..
Step-by-step guide
Go to your site.
In the top right corner, clickSettings.
ClickSite Settings.
Under the Users and Permissionscategory, click Site Permissions → Permissions → Grant Permissions.
5. Select a group to add permissions
6. In the given Invite people to field, enter the user's email address or usernameand select the appropriate user from the drop down menu that appears.