you should be running only one resident anti-virus program at any given time.
here's the best way to change:
make sure you already have the installation file for the new/desired anti-virus program (either in terms of it being on a CD, or having already downloaded it to your computer).
then disconnect yourself from the internet (e.g., by unplugging your Ethernet cable, or turning your router off, or disabling your wireless card).
use add/remove programs to REMOVE your old/UNdesired anti-virus program
and finally, run the installation file to install your new/desired anti-virus.
after the installation is successfully completed, you can reconnect yourself to the internet, then allow the anti-virus to obtain its most recent updates. at this point, if you wish, you can scan your system for viruses.
Windows 7 Pro SP1 (64-bit), avast! v12 Free, MBAM Pro, Windows Firewall, OpenDNS Family Shield, SpywareBlaster, MVPS HOSTS file, MBAE Premium, MCShield, WinPatrol PLUS, SAS (on-demand scanner), Zemana AntiLogger Free, IE11 & Firefox (both using WOT [IE set to WARN, FF set to BLOCK]), CryptoPrevent, Secunia PSI.
[I believe computer-users who sandbox (Sandboxie) are acting prudently.]
Windows Insider MVP 2016 -
Microsoft MVP - Consumer Security 2006-2016Social Media and Community ProfessionalSpywareHammer
I am not a Microsoft or a Dell employee. I am a volunteer.
Windows Defender is an anti-SPYWARE program, not an anti-virus:
"Windows Defender... helps you stay productive by protecting your computer against pop-ups, slow performance and security threats caused by spyware and other potentially unwanted software."
as for your other "form of Norton scan", that could be anti-virus, or anti-spyware, or anti-rootkit, or...
avg 8.0 includes both anti-virus as well as anti-spyware protection. by all means, remove your old [expired!!] Norton anti-virus.
as for the other norton "scan", it depends on whether it's strictly an "on-demand" scanner ONLY, or if it also has a resident module [and in the latter case, what type of resident protection it offers].
finally, I'd say you should leave windows defender alone, unless you notice any slowdowns/conflicts with avg's anti-SPYWARE components.
First, i would recommend you to make the clean uninstallation via add/remove program or download the norton removal tool.
Second, window defender is the anti-spyware. So far, it doesnt has any problem to run with other antivirus or spyware. As earlier post said, you may leave this program to run if you never expereince of slowdown in the performance from your computer.
I would recommend you to run a single antivirus software.....