For a same server upgrade, without version change, the only option is to backup the MAS90 folder, uninstall the old Sage 100, install Premium, then migrate from the MAS90 folder copy. Sage won't let you install multiple flavors of the same version on a server. (That hasn't been possible since v4.5).
Take a full server snapshot in case something goes wrong with the migration and you need to reset and use the old version again.
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Kevin Moyes
Technical Systems Analyst
Munjal White Consulting Co.
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