Increase the file upload limit
Add the client_max_body_size directive inside the http { } section of the /opt/bitnami/nginx/conf/nginx.conf file. For instance, to increase your upload size to 20MB, add the following line:
client_max_body_size 20m;
Remember to restart the NGINX server for your changes to take effect.
$ sudo /opt/bitnami/ctlscript.sh restart nginx
To increase the upload file size limit for PHP, follow the steps described here.