Locate the php ini configuration file by running the drupal status report and clicking on more information:
loaded configuration file value: /opt/bitnami/php/etc
Parameter: memory_limit Value: 64M, 128M, 256M Note the larger the parametr value the less concurrent processes that will run on the drupal instance.
More information can be found at https://www.drupal.org/docs/7/managing-site-performance-and-scalability/changing-php-memory-limits
Instructions at https://www.digitalocean.com/community/tutorials/how-to-configure-virtual-memory-swap-file-on-a-vps