Is there a new version of the form as well?  You should just be able to
publish the new form template to the existing/upgraded forms library.  

As Kalyan's link suggests, changing the location might be possible in the
forms themselves.

If there are a lot of forms, you could also convert the Xml to your new
InfoPath form format.  This would require knowledge of Xml and XSLT to do
this however, so may not be your cup of tea.  If you don't have many forms it
may be time to just bite the bullet and retype the lot - ugh :)  I have more
information on how to do this here:

http://www.infopathkb.com/Knowledge%20Base/How%20to%20manually%20change%20an%20I
nfoPath%20Forms%20Services%60%20template%20location%20in%20an%20existing%20InfoP
ath%20form.aspx

In the case where there are lots of forms, you could even use a utility that
did a global replace of the <?mso...> reference to your new template location.

Gavin.