My site is suddenly running really slowly

It seems like the slowdown was the result of upgrading the server somehow because it only seemed a little slow before I upgraded, and after I upgraded it's unbearably slow. My site is http://artfight.net. Linode support says it's not their problem. Can anyone help me? I'm really new to this so I'm not sure even where to begin, though I did find this article on here called Troubleshooting Memory and Networking Issues, and I'm not sure how to interpret it.

Here's the results of the steps in that article, but it doesn't say what I should do with the info once I get it?

free -m

~~https://i.imgur.com/WDBAmrD.png" />

ps -eo pmem,pcpu,rss,vsize,args | sort -k 1 -r | less

~~https://i.imgur.com/xiWG4xL.png" />

iostat -d -x 2 5

~~https://i.imgur.com/s31PFw0.png" />

After that there's the category "Low-Memory Settings" and "Apache 2 Low-Memory Settings", and those tell me to change some values in some config files but it doesn't tell me what to do after I change those values.~~