How Can You Make Your Mac Faster?!

[Mr. Incredible]

I got an iMac, purchased in 2010, and I have noticed that it's performance has been getting slower as time goes on.

A few months ago I increased the Memory from 4 GB to 12 GB, but it doesn't seem to be improving.

When downloading movie trailers from Apple, it used to be super fast, now it takes even longer, youtube videos take longer to load and sometimes a video doesn't even show up but audio does. I get the spinning beach ball every once in a while, and it's annoying.

Currently, my Processor is: 3.06 GHz Intel Core 2 Duo, and my Memory is: 12 GB 1067 MHz DDR3.

Would I have to increase my Processor to make it faster? But if that's the case, isn't it really hard to DIY?

 

[simsaladimbamba]

Since it worked well before, and doesn't seem to work as well now, there is no need for a hardware upgrade, as there is a more likely solution in solving your problems via troubleshooting it.
First: Performance Tips For Mac OS X

Also open Activity Monitor and select All Processes and then either sort by Real Mem to show you the process(es) using up your RAM or/and sort by CPU to show you the processes slowing down your Mac.

Using Activity Monitor to show you CPU and RAM usage​

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Second: Does it also happen in another, even temporarily created, user account?
Third: Has anything changed internet connection wise since it worked well?

Btw, I have no problems watching 1080p content on YouTube or 1080p trailers from Apple on my 2007 iMac with a C2D 2 GHz CPU or my 2009 MBP with a C2S 2.8 GHz CPU.