Mainly what I would do is that
-Add a CDN:
*Offer higher availability, lower network latency and lower packet loss.
*If your main web server is based in Dallas, users from Europe or Australia must make a number of trans-continental electronic hops when they access your files. Many CDNs provide localized data centers which are closer to the user and result in faster load of the website.
* Boosts performance and saves money, a CDN can distribute the load, save bandwidth, boost performance and reduce your existing hosting costs .
-Switch it to nginx the webserver and optimize it, optimizing will take advantage of all your server resources.
-Tunning on the MySQL configuration
* Enable the log_slow_queries variable
*Configure cache
*Index the most slow/used queries
*Build a configuration based on your server resources and on the usage behavior of your database
I can offer a more extended solution but I need to look at the server side debug for know if there's something else that I can do.