Unless something unadvertised has changed recently, Vegas Pro upgrades have required the upgrade to be from a previous version of Vegas Pro or VEGAS Movie Studio (version 17 or earlier - but not MAGIX Movie Studio versions.) - but just as long that an upgrade from that previous version hasn't already occurred in the past.
If wanting to cross-grade from a MAGIX product, you might want to contact sales@magix.net and ask the sales team if cross-grading to Vegas Pro is possible.
@JOHN-CHEN Hi, go to the Magix website, Log in, go to the bottom of the Vegas page, choose the Upgrade option - 'Buy now' & go through to the next page, there'll be a msg on-screen to say your upgrade has been accepted. You can do this without having to go to the final payment window.
@Dexcon Unless something has changed I upgraded from 'MAGIX Movie Studio versions' to VP18 (Movie Edit Pro as it was then, now it's Magix Movie Studio), that was 5yrs ago but I don't think it's changed.