slow internet but never used to be

Starting with what the "Mayer" suggested is the best way to go I think , but here's few other suggestions: There's a free third party App called "What's Keeping Me". It helps in determining what programs or Apps are using the most RAM. I had a problem with "spotlight" for instance. It was hooked up to "Time Machine" and was constantly indexing my entire hard drive. Besides that , you can click on the Apple symbol and scroll down to "Force Quit" just to see if any apps are running that you thought you already turned off.(There's no need to actually force quit anything unless you absolutely have to ) Any Apps that transcode would use a ton of RAM, for instance. Also, are you sharing your router? If not, is it secure?