That happens to me on the machine I'm using now. At some point I had the bright idea of installing a second copy of DBPro in a different directory. Ever since then the upgrade installer tries to install to that directory. All I have to do (when I remember

) is change the folder name to the one I want. Here's the relevant step on this machine - I always have to delete the string " DGS" from the install location. What do you see when you upgrade, and what directory do you use for DBPro?
Sounds like something similar is happening to you. The only other possibility is that you haven't actually run the installer itself. Sounds daft now but at one point I thought I'd installed an update but in fact had only unzipped the installer. (In other words never try anything important after midnight.

)
If you have successfully run the upgrade installer you should see the appropriate upgrade txt file in your DBPro folder as in my example below:
A full uninstall/reinstall might be the answer though.