How do I optimize my.cnf for my server as my website keep crashing

Hi, I am having a nightmare with constant 504 Gateway errors. I have spent the last week trying to troubleshoot the website (checking plugins etc.) l am now looking at whether it is the server settings. My dedicated server spec is as follows: Usage 1% 6 CPU cores 1.98% / 100% 5% RAM 3.57GB / 64GB 27% Disk space - RAID 1 1080GB / 4000GB My current my.cnf is as follows: # For advice on how to change settings please see # This is the output result: [root@********* ~]# perl mysqltuner.pl >> MySQLTuner 2.1.1 * Jean-Marie Renouard * Major Hayden >> Bug reports, feature requests, and downloads at MySQL: Welcome (specially the conclusions at the bottom of the page). When making adjustments, make tmp_table_size/max_heap_table_size equal Reduce your SELECT DISTINCT queries which have no LIMIT clause Performance schema should be activated for better diagnostics Before changing innodb_log_file_size and/or innodb_log_files_in_group read this: My questions are: 1. Is there anything in those results that would be the cause of my 504 Gateway error and poor performance? 2. What should I change/add to my.cnf to improve the performance for my dedicated specification? 3. If this isn't something you'd recommend I try myself is there someone at Cpanel who can help me tune this and PHP settings to eradicate these problems and speed up performance and what is the cost? I did try changing some settings but then when i saved it crashed so had to revert back to the default my.cnf as shown above. I do hope you can help me as this is destroying my user experience. Kind regards