I have a few problems lined up here which you will probably want to solve.
#1 - Server response time seems a little slow at 2.49 seconds.
#2 - Logo seems to clash with the header.
#3 - Font seems a little small. May be hard to read.
#4 - Grey on grey can be hard to read.
#5 - Using HTTP/1.1. You probably want to use HTTP/2 or HTTP/3 for faster page loads.
#6 - You probably want to use PHP7 (e.g. 7.2 or 7.3) instead of PHP5.6. Both because it's more secure and because it's faster.
#7 - Please stop advertising your version of PHP in the X-Powered-By header.
#8 - You probably want to use Brotli instead of Gzip, if possible as it's a faster and more compact compression algorithm.
#9 - You likely want to avoid using web fonts (e.g. FontAwesome) and want to use SVG versions of them instead as a web font contains countless icons which you will never at the cost of the larger file.
#10 - Use HTTPS instead of HTTP. It's good for security, SEO and performance. Let's Encrypt and Cloudflare are good places to get a free certificate for that.
I can't necessarily point you to all of the solutions, but I can give you some insights into why things are problematic.