WordPress was telling me I didn’t have ‘sufficient permissions’ to update my own install even when logged in as the Administrator.
I had the following line in my wp-config.php file:
define('DISALLOW_FILE_MODS',true);
I was able to apply updates once again after I changed this line to:
define('DISALLOW_FILE_MODS',false);

DISALLOW_FILE_MODS is a constant defined in wp-config. PHP, which disables plugin and theme updates and installation through the Dashboard. It also disables all file modifications within the Dashboard, thus removing the Theme Editor and Plugin Editor.

By default, this setting isn’t specified in the WordPress wp-config.php. If you’ve never set it before, it won’t be there, and you’ll have to add it yourself.

But you need to be careful where you add new configuration settings – you cannot add them to the end of the file.

A good place to do it is to look for WP_DEBUG and add it immediately after this line.

Always make a backup of your wp-config.php, so you can revert back to the original if any changes causes problems.