Lately my Imac is moving very slow. I get the spinning color wheel and it's very slow to go to the next screen. What happened? Is there a way to clean out the computer?

Download the freeware diagnostic, EtreCheck. Use it to provide you with information about your computer. By studying it carefully you may get some ideas on why your computer is running slow. Here are some additional links:

OS X El Capitan- If your Mac runs slowly

Slow Mac Performance? This Article Solves It!

17 Reasons Why Your Mac Runs Slower Than it Should

Runaway applications can shorten battery runtime, affect performance, and increase heat and fan activity.

If you don't have enough memory installed for the number of applications you have loaded, then consider quitting some to free up more memory. The more memory you have installed the better will be the computer's performance, all other things held constant.

Are you really using a 10 year old iMac?

I don't like the suggestion of 'cleaning out' the computer. It has all the sense of using anti virus and other unnecessary stuff.

We will look at the Etre check if you publish it and come back with some guidance.