Gary, when you start the download, your XDA is still open.
You are told to close it. Sometimes a close fails in MS windows so the install finds a locked file.
A reboot, as @Christine Farrelly Christine says, should work as a Windows log off and on again, possibly even logging in as Admin.
The sledgehammer is to open Task Manager, right-click on DesignerPro.exe > End Task.
You might be in a Catch-22.
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