carlahelp, you definitely don't run more than one anti-virus program - they do not play well together. Windows Security Essentials is a full anti-virus program - go to the link Jenny provided and read more about it if you're not sure. If you are no longer going to use AVG or Avira, make sure you uninstall them first.
If you have a paid-up copy of AVG that is still active, check with AVG to see if you can transfer the license to another computer - usually they don't let you do that unless the license is already for more than one computer. But check with them to be sure.
You can use Malwarebytes along side your anti-virus program with no problem.