Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
Do Not download any software from anywhere to improve the performance of your Mac. They does more harm than any good. There are many troubleshooting steps you can do it yourself which improve the performance of your Mac.
First reset the PRAM and NVRAM of your Mac. This will clear some old temporary memory and speed things up.
Shut down your Mac
Restart and immediately hold down Command-Option-P-R keys at the same time
Hold the keys down until the computer restarts and you hear the startup sound for two or three times.
Release the keys and let the Mac bootup.
Then you can run Disk Utility and this will fix corrupted system files, fix files permissions etc. Turn off your Mac by holding down Power button for 10 seconds. Then turn it back on and immediately hold down Command and R keys at same time for 20 seconds and this will boot your Mac to the Mac OS X Utilities screen. From there, click Disk Utility. Select your hard disk at left column (Macintosh HD or hard disk name). Then click Verify Disk (under First Aid). If asked to repair, click Repair Disk. Then click Repair Permission.
(If you are using latest Mac OS X El Capitan, then you will not see Repair Disk option in Disk Utility. Instead click First Aid button and run it. Repair if asked)
You can also reinstall the OS X. Reinstalling the OS X will replace old system files with new ones without affecting your personal files. Reinstalling will only replace the system files.
Restart your Mac and immediately hold down Command and R keys at the same time for 15 seconds and this will boot your Mac to the Mac OS X Utilities screen. From there, click Reinstall Mac OS X. Then follow the instructions to reinstall your Mac OS X.
If that didn't work, then restart your Mac and immediately hold down Command, Option and R keys at the same time for 15 seconds and this will boot your Mac to installation screen. Follow the onscreen instructions to reinstall.
In some cases, your Mac will start to slow down if the hard drive itself is failing. So I want you to backup all your important files to an external hard drive or USB drive for safety. If your Mac's performance doesn't improve after doing all the steps above, that means either the hard drive itself is failing or the hard drive partition is corrupted.
So there is one thing you can try. Backup all your files, then erase the hard drive and install a fresh OS X. You can erase the hard drive from Disk Utility by booting into OS X recovery and then erase from there. After erasing, just click Install OS X. If you still experience slow downs after fresh install, that means the issue is with the hard drive and you will have to replace it.
Print/Note down these instructions. So you can take your own time (doing all these will several hours) and do these steps at your convenience and get back to me if you need any help and I will continue to help you here.