try opening a terminal in the directory containing the file and typing:
sudo chown user:user filename -R
i think thats the right command. replace the word "user" with your username e.g. berry:berry and "filename" with the name of the file. that should do it. ill double check the command. if its not right ill edit this. if it is then ill just leave the comment as is. again, this is based on linux so no garuntee but luckily the terminal in mac is very similar. best of luck