All these steps should be done as root user. Adminer will be installed beside phpMyAdmin. So you would be able to use both. If you want, you may remove phpMyAdmin manually.

Adminer installation:

mkdir -p /usr/share/adminer
wget "https://www.adminer.org/latest.php" -O /usr/share/adminer/index.php

NGINX:

echo "location /adminer {
    alias /usr/share/adminer/;
 
    location ~ ^/adminer/(.*\.php)$ {
        alias /usr/share/adminer/$1;
        fastcgi_pass 127.0.0.1:9000;
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $request_filename;
    }
}
" > /etc/nginx/conf.d/adminer.inc

APACHE:

echo "Alias /Adminer /usr/share/adminer
Alias /adminer /usr/share/adminer
 
<Directory /usr/share/adminer/>
   Order Deny,Allow
   Deny from All
   Allow from All
</Directory>
" > /etc/httpd/conf.d/adminer.conf

Reload or restar nginx and apache:

service nginx restart && service httpd restart