Can't change permissions

Hi! I'm trying to move some of my pictures to an external hard drive to free up some space and am running into issues. When I try to move a photo to the hard drive I get the grey circle with the line through it. I verified I logged in as my admin user. When I try to go into the Sharing & Permissions section for my hard drive it says "You can only read" I have clicked the lock and put in my password and tried to change the permission so everyone can read & write but it keeps telling me "The operation can’t be completed because you don’t have the necessary permission."

Any ideas?