Wordpress will not update

Hi guys, I am having a problem with my Wordpress site, it will not update to 3.5.1. When I go through the update process within Wordpress, it says that it is updated, but when it go’s back to the dashboard, it says its still running the old version and asking me to update. Same with my plugins, any ideas why this is happening? I have tried deactivating all my plugins and changing theme to twenty10.

Redownload the wordpress files and upload the files again and reinstall.

you go to your ftp, and check wordpress folder and change its permission and then update it.

Maybe it will be better to back up your database and then completely upload a WP into the folder by ftp?