If your hosting provider enabled the option to change the PHP values from the Cpanel just login to your panel and change the options there.
Otherwise try the following methods. Be aware that this section requires advanced knowledge.
Increase the Max Input Vars Limit
The max_input_vars directive can be configured in .htaccess, php.ini or wp-config.php file. We recommend to increase default value to 3000. But if you have a lot of menu items try 5000 or higher.
Here is how you can do it:
php_value max_input_vars 3000
max_input_vars = 3000
@ini_set( 'max_input_vars' , 3000 );
Increase Maximum Execution Time
You may receive a message such as “Maximum execution time of 30 seconds exceeded” or “Maximum execution time of 60 seconds exceeded”. This means that it is taking to longer for a process to complete and it is timing out. There are a number of ways to fix this error.
php_value max_execution_time 300
max_execution_time = 300
Increase Memory Limit
php_value memory_limit 256M
memory_limit = 256M
Should you not feel comfortable in trying the above methods, or the above did not work for you, you need to contact your hosting support about having them increase your PHP values.