Why can't I change the privileges for this disk on my mac?

I'm trying to change the privilege for a disk from "read only" to "read and write". I have done the steps I've seen online and I am an admin, but when I try to change the privilege I get a message about how I don't have the necessary permissions.
Answers

Anonymous

use the terminal command and make sure you use sudo before your command. It's short for superuser do So if you do the command sudo chmod 755 /dev/sda1/ or wherever your drive is located you can change the permissions so try this Drag your drive into the terminal and that will show the location, then copy and paste the location in the command sudo chmod 755 (paste location)

Anonymous

you have to take rights at a higher level , sign in as an administrator and give yourself permissions as needed, you need to take ownership sometimes to take permissions