If you just switched from PC to Mac, many things are new for you. Even WordPress errors. You can quickly start being frustrated from beginning when even things which used to be easy on Windows are now hard on Mac. Updating local WordPress installation is one of them.
When I had tried to update WordPress on my XAMPP, updating process thrown an error about denying of file change. The solution for problem is actually very simple and its root is in a way how OS X manage files. OS X is based UNIX so every update/download of WordPress installation require permission to write and update files. This can be easily fixed setting read and write rights for all groups at WordPress installation folder. Just type following command to terminal
$sudo chmod -R 777 /Applications/XAMPP/htdocs/YOUR_WORDPRESS_INSTALATION and all subfolder and files within your WordPress installation will recursively set themselves for rewritable by all groups.
This is actually terrible solution for public server from point of security. But at local network, I guess, setting access to 777 just for specific folder does not consider any harm or potential treat.