I'm not a developer and our original developer doesn't know how to fix this, so I'm pretty desperate, hope you guys can help!
I have ran the website through different analysis:
Pingdom: http://tools.pingdom.com/fpt/#!/dlRIXt/www.sanefitnesshk.com
Google Developers: https://developers.google.com/speed/pagespeed/insights/?url=http%3A%2F%2Fsanefitnesshk.com%2F&tab=desktop
I've already installed W3 Total Cache.
If you need any more information, please don't hesitate to ask as I don't even know where to start to fix this problem.
Thank you so much!