Website not working after 3.6 update

I have just updated wordpress to 3.6 and have encountered the following error:

Fatal error: Call to undefined function get_post_format_slugs() in /websites/123reg/LinuxPackage23/ox/an/ad/oxanadodon.com/public_html/website/wp-includes/theme.php on line 1262

I have no idea what to do and I can’t even login to my wordpress dashbaord.

Website: https://www.oxanadodon.com

Please help!

[duplicate post: https://www.ads-software.com/support/topic/website-not-working-after-36-update ]