Suppose that a project has completed and you no longer want the team to add or edit the project’s supporting documents. The flexibility of SharePoint 2103 gives you the ability to easily make changes to permission level of an individual or a group.
Edit site permissions for an individual or group
On the Home page, click the Settings button (the small gear icon next to the name of the logged-on user). On the menu that appears, click Site Settings.
On the Site Settings page, in the Users And Permissions section, click Site Permissions.
On the Permissions page, if the site is inheriting permissions, click Stop Inheriting Permissions, and then, in the pop-up message box that asks you to confirm the change, click OK.
Select the check box next to the group or individual for which you want to edit permissions.
Click Edit User Permissions.
Clear the current permissions check box and select a different one.