Can’t access Update core

I can’t access my update-core

Do you mean you can’t access WP dashboard (admin area)? Please elaborate.

You can always try MANUALLY updating. Here are the instructions:
WP:
http://codex.wordpress.org/Updating_WordPress#Manual_Update

Plugins:
https://codex.wordpress.org/Managing_Plugins#Manual_Plugin_Installation
https://www.wpbeginner.com/beginners-guide/how-to-manually-update-wordpress-plugins-via-ftp/

Theme:
https://codex.wordpress.org/Using_Themes#Adding_New_Themes_Manually_.28FTP.29

but I Can’t go to update section and also the update icon isn’t showing above. also the button to add new plugin isn’t showing. I Can’t upgrade my wordpress.

If like to troubleshoot, try:
– to disable all plugins, and use one of the default (Twenty*) themes. If the problem goes away, enable them one by one to identify the source of your troubles.

– If you can install plugins, install “Health Check”: https://wordpress.org/plugins/health-check/ On the troubleshooting tab, you can click the button to disable all plugins and change the theme for you, while you’re still logged in, without affecting normal visitors to your site.

Have you tried troubleshooting as suggested in my previous reply?

– disable all plugins, and use one of the default (Twenty*) themes. If the problem goes away, enable them one by one to identify the source of your troubles.

– If you can install plugins, install “Health Check”: https://wordpress.org/plugins/health-check/ On the troubleshooting tab, you can click the button to disable all plugins and change the theme for you, while you’re still logged in, without affecting normal visitors to your site.