You can do a couple of things, but the basics will be chmod and chown. Chmod changes the permissions of the file or folder to allow rights on a user, group, and world access. Chown changes who owns the file or folder.
From the command line you could use
chown -R to change ownership recursively for all files and subfiles to your username. Or, better yet, you could change the file permissions similarly using
In octal notation doing something like
chmod -R 777 ~/Sites will make it readable, writeable, and executable by everyone on the machine (not necessarily the best way to go). chmod -R 755 would make it writable, executable to the owner and readable by everyone else. There's lots of examples and ways to do this.
You may want to look into users and groups to avoid making it all world executable, and not annoying you everytime you want to modify a file.