Actually, that link will not produce the desired effect, since a clean install is always recommended over an upgrade. To do what you want, select manual at the partitioning stage. If you selected one of the default install options last time, you will see only a single partition formatted with ext3. Select this partition > Edit > Format YES, use as / and you're all ready to go, it will delete any data you have stored in your mint home directory. If you have a more complicated partitioning setup, read the how-tos on partitioning here in the forums (usually written by "Fred") for more info.
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