If you want to upgrade your Magento-Store there are many different ways to do that. I prefer this one:

If you want to install a fresh copy of a new magento version – and you want to transfer your products and customers from your old magento store you can do it this way:

• disable cache in your actual magento store
• make a copy of your actual magento database
• install this dump in a new database (I call it „dump-database“)
• Download the latest version of magento.
• Start the setup routine.
• When Magento asks for the access data of your database, use the acess data of the „dump-database“.
• Magento will automatically upgrade your database to the newer one.
• Copy your theme, make sure it will run on the newer Magento-version.
• Copy your media folder to use all images of products and categories and wysiwyg.
• Install all the extensions you used in your old store again – make sure, they will run on the newer magento version. If there are newer downloads available, use them.
• Reindex data

If everything works fine – enable cache is the last thing to do…