Windows 10: Best Free AV for Old PC?

I have an older Windows 7 desktop that I need a free Antivirus for, one that's light on system resources preferably. I tried MBAM and it uses up quite a bit of CPU, my old PC would run loud when I had MBAM on it. I need something lightweight and completely 100% free.

 

deleting old AV from my PC.

Name of 'old' AV is: ??????

 

deleting old AV from my PC.

I am running W10 and recently changed AV provider. I uninstalled the old AV but have noticed a folder in program / common folder relating to the old AV provider and cant delete it as it says I need administrator permission - I am the administrator. Its
not causing any problems but will be taking up some space so I just want it gone, how do I delete it?

 

PC Build Steps

Ok just because I like steps i am going to create some steps. Please give me the stamp of approval/disapproval

• Install system in case
  • Remember to connect SSD and optical to same SATA ports on motherboard
• Turn on PC
• setup HDD
• run blend test in prime95 for 30-60 min
  • run realtemp at the same time

• While in Prime95 test
  • if CPU goes above 70c in RealTemp, I have a leaky CPU
  • if my system locks up or blue screens, there is an instability in the system somewhere
  • if my system does not lock up or blue screen, my CPU is not damaged and I am in the clear!

What do you guys think??