I just got my computer repaired and when I booted up I found that I have malwarebytes' Antimalware software. I reinstalled CA Security into my computer and kept the malwarebytes' too. Question, could both software slow down my computer... and should I keep both software? I'm not sure about this, help!

You can open malwarebytes and in the settings tab, you can uncheck to auto run with the computer on startup.

What you can do is to keep malwarebytes and then just run it manually when you want or need to - just not run on startup