A common error you can come across in WordPress is a PHP memory limit error. This happens when WordPress doesn’t have enough memory to achieve what you want. It can be caused by poorly written plugins that will continue to run a procedure until the installation runs out of memory.
Since version 2.5 there is a wp-config.php option WP_MEMORY_LIMIT which allows you to configure the maximum amount of memory that can be used by PHP.
When you change this option in the wp-config.php it will only affect your WordPress site and not any other PHP sites.
To change the WordPress memory limit you just add the following into the wp-config.php.
If this doesn’t change your allocated wordpress memory limit your hosts may not allow you change this setting, if this is the case you should contact your hosting company