WordPress管理员失去了一些管理员权限

On my WordPress site, the admin account has lost some admin privileges. Like I can't add new plugins and themes, there's no menu for this. And I can't update core WordPress. It says,

WordPress 4.8 is available! Please notify the site administrator.

So How Can I get back my site administrator power?

Please see this image -

Can't add plugins ![two muppets][1]

Any help would be highly appreciated.

Regards

The site administrator would be the account that you used to create Wordpress in the first place, so the installation. If you did lose that account you should either try forgot password or edit it from the database. Do keep in mind that the Password in Wordpress is encrypted with a key that is needed. So you'll have to generate a new one on a page like: link