Yesterday we talked about how by default all the Users that gets added to a default Members group gets Capabilities to “add, edit and delete lists” in your SharePoint 2013 Site. Read the entire findings at SharePoint 2013 – Adding Users to default Members group? Change the “Edit” Permission level first!. So now that we Identified that we have a problem here, lets look at How to Change the default Permission Level for this Members group in SharePoint 2013 “Contribute”.
Firstly, not all Members group(that are Created by default) has “Edit” permission level by default.It depends on the Site Template that you have used to Create a Site. But if it is Edit, you must Change it to Contribute to avoid users deleting the entire List or Libraries.
1. Navigate to Navigate to Site Settings -> “Site Permissions” (under Users and Permissions).
2.Next, Look for the group that you need to Change the Permission level for. In our case we need to edit “Team Site Members” group’s permission level to Contribute.
3. Once you find the group, select it using the Checkbox available right next to it.Next in Ribbon select “Edit User Permissions”
4.In Edit Permissions page uncheck “Edit” permission level and select “Contribute”. Click Ok once done.
Original article : Here