Enable SharePoint Designer on SharePoint 2010 Site Collection

To Enable SharePoint Designer on your SharePoint Site Collection

1. Go to Site Settings > Site Collection Administration > SharePoint Designer Settings
2. Select Enable SharePoint Designer
3. Select Enable Detaching Pages from the Site Definition
4. Select Enable Customizing Master Pages and Page Layouts
5. Select Enable Managing of the Web Site URL Structure
6. Click the OK button to save the changes.