Method 1: Edit file .htaccess:

Add the following to .htaccess (Make sure you back up .htaccess before you edit it):

php_value max_execution_time 300

Method 2: Edit file wp-config.php:

Add the following to wp-config.php:

set_time_limit(300);

Method 3: Editing php.ini

Add the following to php.ini:

max_execution_time = 300

Read more about Maximum execution time exceeded on WordPress.org.