Improve WordPress website performance

Your task is to improve website performance, especially on mobile devices, by looking at the following areas:
- Eliminating render-blocking resources
- Using HTTP/2 for all resources
- Reducing the impact of third-party code
- Minimizing main-thread work
- Optimising cache
- Reducing HTTP requests
- Adding Expires headers
- Ensuring that static components are requested with cookie-free requests
- Compressing components with gzip to reduce the size of the HTTP response
- Reducing DNS lookups
This is a live website, so all changes need to take place on a test site before implementation. In addition, website has to be backed up for contingency.
Performance needs to improve by a minimum of 50% from the current state based on the attached performance statistics from https://www.debugbear.com/, https://tools.pingdom.com/ and https://gtmetrix.com/
First Contentful Paint: 2.9 s
Largest Contentful Paint: 2.9 s
Total Blocking Time: 1,100 ms
Speed Index: 10.6 s
Load time: 22.89 s
Requests: 132
Time to Interactive: 3.1 s
Full TTFB: 1.16 s
CPU Time: 8.54 s