Hey Guys
I am a computer tech and have worked on this stuff for 15 years, if you are going to upgrade Windows, do go to Win7, stay away from 8-8.1, it is comparable to WinME, (the worst POS they ever made). If you can wait they are now working on Win10 that will detect if you are using a PC and make your desktop look like the Win 7/XP desktop, if you install it on a tablet then it will look like Win 8.
Now for AV (Anti-Virus) stay clear of Norton as it is a system hog and you usually need to download special software to remove old version, the best ones I have found are Kaspersky, BitDefender, and ESET NOD32.
Along with your AV you will need an Anti-Malware tool, the best one of these is free and is called Malware Bytes, the only downside to it is you can not configure the freebie, it must be updated and run manually, generally once a week is good. If you find that you don't have the time to do the manual stuff you can buy a version that will let you setup scan and update times similar to your AV.
Hope this helps.
Gary