Thank you for using Bitnami. Upgrading the PHP version in a running Bitnami instance is not an easy task, it requires to compile PHP and all the components that requires it. The easiest way to upgrade the PHP version is by migrating your suiteCRM installation to a new server which has the new version of PHP.
You will need to launch a new instance with LAMP 7.x, deploy the SuiteCRM version you have (you can find more information here) and migrate the data from the old installation to a new one
I hope this helps