What should I do to lower CPU usage?

So my computer keeps running at 100% CPU usage. I'm lucky enough for this to load it's so slow. So I check the task manager. The main reason are two things. First was Firefox. I got the fasterfox add-on but after realizing that was the issue, I uninstalled it. So now the issue is avp.exe. From what I've read, it's a Kaspersky program. Now I haven't used Kaspersky for a year now and it should be renewed and updated but I don't plan on renewing it. The reason why I keep it on my computer is that it's the only online security I have. I have MBAM free version but I don't think that does internet protection.