Recently I upgraded from 10.6.8 to 10.11.6 El Capitan and also changed from AT&T to CableOne because my imac was running so slow. Everything seemed to be running OK, but now I'm running really slow. I can't figure out what I have done to cause this or what I need to do to fix it. My hard drive is about 1/3 full. I think maybe there are some things running in the background that I don't know about that may cause my problem. What would be my first step to bringing me back up to speed?