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Sometimes prior versions can cause problems. It is best to export the database, uninstall the MySQL server and other components, and restart so the services are removed. You also want to Make a note of any MySQL users (other than root), as you may want to re-create these to ensure consistency.
If you have trouble upgrading (there is one step where an old password is requested, which can be difficult to figure out), you should delete the MySQL data, which is the MySQL folder under C:\ProgramData\ in Windows 7. The fodler is hidden, so you need to type it into the address line of Explorer.
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