An upgrade with an unmodified board should be that simple.
You shouldn't need to fool with permissions if you are replacing files. If things don't work, then you can go back and check file permissions... but in reality if you are replacing files, you should be fine.
Actually though... you'll need to chmod the new /images/graemlins directory... as well as /images/icons and /images/newicons as the newest version allows for you to add/edit graemlins and icons....so the permissions on these new folders will need to be 777.
Even if you messed up this step, that wouldn't affect anything major. You'd receive an error if you tried to add graemlins/icons etc.
But yes, it should be that simple.
