If you are running on SQL, a backup of the database can be done from the management console like any other database backup. However, it is a bit unclear what you're trying to achieve. Are you upgrading your NPM or is there an issue that you're trying to correct, or are you looking to migrate to a different machine? Is your DB housed on the same server as your NPM install or is on a separate server?
Edit: I was trying to look for a link before posting, but I have found it now.
In the bottom, middle section called "Migration Guide" there are a few articles that may help you out.
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