Installing AVG Internet Security

I have downloaded the file for AVG Internet Security, but when I attempt to install it I get a message telling me that another version of AVG is already installed and is not compatible with Internet Security.  Frankly, I think I have multiple accounts with AVG but they continue to bill me for separate accounts.  I also have AVG Pro and Zen on my desktop. 

Any assistance will be appreciated.  I'm not a computer expert by any means. 

Thanks in advance.