How Can i Change Permissions to "Read all Write all" Globally on my external HD?

So heres the deal..

i used to have a bunch of files on my hard drive before i sold my mac pro
i backed everything up on an external hard drive so i can keep it until i received my imac. now i have my imac, and when i try to transfer over the files to my imac, or another external hard drive, sometimes the copying stops and says something along the lines of "you do not have permission to copy this file"

so i guess some of my files got messed up, putting them in "Read only" mode.
i know i can go to "Get info" and then manually change it to "read and write" mode but honestly theres so many files it would take a lot of time.

is there a script, or an app i can run that could scan my whole external hard drive so it will go thru each file in their own specific folder and change the permissions to "read all write all" without me doing it manually one by one?

spinnerlys said:

Select HDD > GET INFO > change permissions for user to what you want it to be, click that red "circled" icon in the image below and the blue option I highlighted and put a red rectangle around.

Click to expand...

thank you!

quick question.

i have a box (which is currently checked) that says
"Ignore ownership on this volume" .. should i leave this checked?