With www and without www versions
You need to put a
301 permanent redirect in place pointing the non www version to the with www version (as you said above you want to promote with www).
On a Apache server this is done in the .htaccess file (as explained in the article linked above).
On Window servers there seems to be a problem making it clear to the web hosting company that it
MUST be a permanent 301 redirect.
The instructions I found so far for a Windows server appear to be for the actual server (which you probably don't have access to).
Ask the hosting company how to do this/get them to do it.
Once told it's been done, check the
headers to see that they have in fact used a 301 permanent redirect.