problem with AVAST

Hi.
I have downloaded the new version of AVAST anti virus for Linux. I have the .deb file on my desktop. I am unable to install it. I have used Ubuntu Software manager and it says " wrong i386 architecture". I tried to install from Terminal, but it says " no file or directory". Please help.
I am not good with command prompt and now learning. It would be great if the solution provided with the complete command lines.
Thanks.