You can speed up your website by using the plugin
WP Fastest Cache Plugin : https://wordpress.org/plugins/wp-fastest-cache/
Autoptimize : https://wordpress.org/plugins/autoptimize/
*Please note that with this method, it doesn't guarantee that you will get 100% of the score from speed tester. However, the score should improve a lot. The score will depend on image optimization too so you may seek for third party plugin to do image optimization but beware that it might drop your image quality, this is on your decision. And lastly, using CDN might improve your score too but you have to seek for third party service for this(You can check out CloudFlare free CDN service).
*Please also note that some third party plugins might not work with the minifying setting that we recommend so if it doesn't work, you may skip this setting. But it 100% works with the theme itself.
Every time you made changes on your website, you should purge the cache too.
WP Fastest Cache
1. In Setting page, follow these settings.
2. Go to Exclude menu and add a new rule in Exclude Cookie section.
Select Contain and fill 'Subscriber' in the field. (This to prevent caching when customers login. It will be useful in theme that require membership functionality such as Chariti, Travel Tour, Clever Course..)
In the JS,CSS and HTML tab, follow these settings.
If you're using CDN, we recommend to leaf the CDN field in Autoptimize empty go to use CDN setting in WP Fastest Cache instead.