How to improve performance?

[BBQ BOY]

I have a 4 year old iMac and it is gradually slowing down. Many times the computer just freezes and has that processing pinwheel going around and around and around...... Y'all get the point. Then there are ties when it is fast then suddenly slows down and proccesses for about 10 seconds or so then is ok.
Is there software I can buy that may help clean up the system or something in preferences I can do?

 

[Spike88]

As a suggestion, "load up" your iMac with normal load. With your "usually loaded" apps in the background, use System Preference - Activity Monitor and provide screen prints of its System Memory, CPU, Hard Disk and Network screens. This will help us understand if your machine is CPU congested, Memory congested, HDD congested or Network congested.

Also... A few might suggest "resetting" permissions on the HDD. Or, resetting SMC values. For now, do provide us print screens of your "average loaded" iMac. re: Print Screens from Activity Monitor application.

 

[KylePowers]

What kind of specs are on that 4 year ol' iMac? Maybe upgrading it could help? More RAM? Faster hard drive?