Can't edit hard drive

I have a Seagate Backup Drive that I use with my MacBook Pro. I've only used it on this computer.

All of the sudden the finder window says that I only have permission to read this. I have not changed a thing on either my computer or my hard drive. The only thing that I did was update to Sierra 10.12.6.

On other forums it says to click on the lock icon to change the permissions, but it's not even showing up. Please help. I NEED to access these files!!!

With the external icon on the desktop, single click and select Edit > Get Info and the padlock should appear on the bottom right of the window. Make sure external hard drive icon is on the desktop, right single klick on Edit > 'Get Info', click on padlock and enter your password and change beside your name and system 'Read & Write'.

If no joy keep us posted.