WordPress：加载速度非常慢

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=https%3A%2F%2F2.zoppoz.workers.dev%3A443%2Fhttp%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!