Mac: Change Permissions of Entire Folder Contents

Step 1: Go to the parent folder that holds your files.

Step 2: Hit Cmd-I to open the info window.

Step 3: Expand the "Sharing & Permissions" section.

Step 4: Click on the lock in the lower-right corner and enter in an administrator's password.

Step 5: Edit the permissions of the folder so they match what you need.

Step 6: Once the permissions are edited, click on the gear icon and select "Apply to enclosed items".