Fix Wordpress automatic upgrade Fatal error: Allowed memory size of 8388608 bytes exhausted....

This means that the server is not allowing to process the size of the data than its maximum allotted size. The error normally occurs when PHP tries to process a big database records or when importing or exporting. Here are the fixes. Try one by one and check

1. Increase the memory limit setting in php.ini e.g. (memory_limit = 64M ;). Many hosts may not allow this.
2. Increase the memory limit via .htaccess e.g. (php_value memory_limit 64M). Many hosts may not allow this.
3. Increase the memory limit via wp-config.php .Put the below code right before the 'stop editing' comment

ini_set('memory_limit','64M');