zee,

When you download, the system asks YOU to pick the folder and directory where it will be stored.

I suggest that you put it somewhere easily located.
I created a Download folder on my C drive specifically for downloads.

You can look on your hard drive under the main hd/windows/temp or hd/windows/internet files
Look for the Avast folder.

Anyway, even if you have a set of files in the Temp folder, they can be easily cleaned out.

Do as Technical advised…download a new copy and save it just in case you need to reinstall it at a later date.

Good luck.