Use HTTP/2
HTTP/2 is a more efficient protocol, that can handle multiple requests at once and reduce the time it takes for the assets of a page to be downloaded to the visitor's browser.
If your host does not support HTTP/2, the report will show an audit that estimates the performance improvement if the page were to support it.
If you see this opportunity in the report, your website or some of the assets that are being used on your website are not supporting HTTP/2. Instead, they're still using an older HTTP protocol, which is not very performant.
In order to address this opportunity, you should make sure your website is using the HTTP/2 protocol.
This is not something that can be set at WP Rocket’s level. HTTP/2 needs to be configured at the server, so you will need to ask your hosting provider about this; or use Cloudflare and enable its HTTP/2 feature in the Network tab; Alternatively, you can also use our service, RocketCDN, to address this opportunity regarding your own hosted assets.
Please find more information about this audit, in Google's documentation.