>>>None of the free ones are worth a light and often cause more issues than they solve
Absolute rubbish!!!
. . . because
(a) the free ones are simply the anti-virus components of full commercial suites anyway (i.e. they're exactly the same as if you bought the entire suite) ; and
(b) independent tests repeatedly find that free anti-virus solutions are at least as good (if not better) than paid-for programs.
Some commercial suites are notorious for slowing some computers to a crawl. (Norton had terrible problems for a while. Then their software got considerably better but the most recent editions still seem to be slowing computers down. If you really must use a commercial program it's Kaspersky that constantly gets the best ratings in the technical press).
However, while AVG is good, it's not what I'd go for just now, as it's Avast that keeps coming out top in reviews published in the technical press:
https://www.avast.com/en-gb/index
Download the Avast set-up file now (but don't install it now unless you want to).
At some time during the next fortnight:
1. Uninstall McAfee by following the instructions in the middle of this page:
https://service.mcafee.com/FAQDocument.aspx?id=TS101331
2. Download and run the McAfee Consumer Product Removal (MCPR) tool, following the next set of instructions on that page
3. Run the Avast set-up file.