Hello Duchess,
You should be able to publish to an existing library in the Publishing Wizard, and select the library you would like to publish over. However, do so with caution. Here are a few things to check before doing so:
1. Is the form template 2007 (IP 2010 form will NOT work on a 2007 site, but you can change the compatibility)
2. Is there existing XML in the library that should not be overwritten? If so...
3. Is the schema of the main data source the same? If not...
4. Using content types will allow both forms to exist in 1 library. http://www.infopathdev.com/blogs/jo-anne_alfafara/archive/2010/10/06/side-by-side-versioning-with-content-types2.aspx
5. If the old data and form are irrelevant, simply publishing to the library should do it.
Please let me know if you need more help! Details on your scenario will help in guiding you in the correct direction.
Bre