Remove the index.php on WordPress permalink

Using FTP go to the main directory of your website. public_html folder.

Download .htaccess .. Back it up.

Then delete .htaccess on your directory.

Then go back to the PERMALINK setting, and change it.
Then upload your .htaccess again.

Everything should work.

BUT If it doesn’t work…

Put this code on your .htaccess file

<IfModule mod_rewrite.c>
 RewriteEngine On
 RewriteBase /
 RewriteCond %{REQUEST_FILENAME} !-f
 RewriteCond %{REQUEST_FILENAME} !-d
 RewriteRule . /index.php [L]
 </IfModule>