While using the site’s hosting control panel (known as cPanel), I noticed an option called Optimize Website.
When you click it, you can turn on Gzip compression. Gzip is exactly the same concept as the tools you might use on your computer to shrink the file size or combine several files into a single compressed archive.
By default, the setting is probably Disabled. Change it to Compress all content. Run Yslow again.
All right, so I didn’t manage to tip the overall score from C to B (or A), as happened on another site that uses another theme. But we fixed one more issue that helps users to load the page faster.
I have not had luck using a plugin such as WordPress Gzip Compression by James Socol because it didn’t achieve its stated purpose. The cPanel option did.